COHESION.

Cohesion. THE corpuscular forces, on which the mechanical properties of the aggregates of matter depend, have been in some measure considered, as far as they relate to solids, in the articles BRIDGE and CARPENTRY of this Supplement (P. 497, 622): there are however other modifications of these forces, which are principally exemplified in the COHESION or FLUIDS; and which afford us a series of phenomena, highly interesting to the mathematician, on account of the difficulty of investigating their laws, and of considerable importance to the natural philosopher, from the variety of forms in which they present themselves to his observation.

SECTION I.—Fundamental Properties of the Cohesion of a Single Fluid.

The three states of elastic fluidity, liquidity, and solidity, in all of which the greater number of simple bodies are capable of being exhibited at different temperatures, are not uncommonly conceived to depend on the different actions of heat only, giving a repulsive force to the particles of gases, and simply detaching those of liquids, from that cohesion with the neighbouring particles, which is supposed to constitute solidity. But these ideas, however universal, may be easily shown to be totally erroneous: and it will readily be found, that the immediate effect of heat alone is by no means adequate to the explanation of either of the changes of form in question.

There can never be rest without an equilibrium of force: and if two particles of matter attract each other, and yet remain without motion, it must be because there exists also a repulsive force, equal, at the given distance, to the attractive force. If we imagined the atoms of matter to be impenetrable spheres, only resisting when their surfaces came into actual contact, it would follow, that the degree of repulsive force exerted at the same distance must be capable of infinite variation, so as to counterbalance every possible modification of the attractive force, that could operate between the particles. In this there would be no mathematical absurdity, and it may sometimes even be convenient to admit the hypothesis as an approximation: but we know from physical considerations that the actual fact is otherwise. The particles of matter are by no means incompressible: the repulsion varies indeed very rapidly when they approach near to each other; but the distance of the particles, and the density of the substance must inevitably vary, in some finite degree, from the effect of every force, that tends to produce either compression or expansion.

In elastic fluids, the law of the repulsive force of the particles is perfectly ascertained; and it has been shown to vary very accurately in the inverse ratio of their mutual distances. It is natural to inquire whether this repulsive force, continued according to the same law, would be capable of affording

Cohesion. the resistance exhibited by the same bodies in a liquid or solid form, and holding the cohesive force in equilibrium: but in order to answer this question, it would be necessary to determine the law of the variation of the cohesive force with the variation of the density. Now if this force extended to all particles within a given distance of each other, whatever the density might be, the number of particles similarly situated within the sphere of action being as the density, and each one of this number being attracted by an equal number, the whole cohesion urging any two particles to approach each other would obviously, as Laplace has observed, be as the square of the density: but since this cohesive force would increase, with the increase of density accompanying compression, more rapidly than any repulsive force like that of elastic fluids, there could never be an equilibrium between forces thus constituted: for, as Newton has justly remarked, the force of repulsion must be supposed to affect the particles immediately contiguous to each other only, their number not increasing with the density. Nor is there any reason to infer, from the phenomena of cohesion, that this force extends to a given minute distance, rather than to a given number of particles, as that of repulsion appears to do. It would indeed be possible to assign a law for the variation of cohesion, which would reduce the repulsion of liquids and of elastic fluids to the action of the same force, without any other modification than that which depends on the mutual distance of the particles; but this law is in itself so improbable, that it cannot be considered as affording an admissible explanation of the phenomena; for it would be required that the force of cohesion should diminish, instead of increasing, with every increase of density, and with a rapidity 19 times as great as the repulsion increased. For the height of the modulus of elasticity of all kinds of gaseous substances remaining unaltered by pressure, that of steam would still be only one twentieth as high as the modulus of elasticity of water, even if the steam were compressed by 1200 atmospheres; and the resistance to any minute change of dimensions would be twenty times as great in water as in steam of equal density, and the variation of the repulsion would be in the same proportion. It is therefore simplest to suppose the repulsion itself to be also twenty times as great, and the cohesion little or not at all altered by the effect of a slight compression or extension: and we shall have no difficulty in imagining this abrupt change in the magnitude of the repulsive force to depend on an increase of the number of particles to which it extends; supposing that when cohesion begins to affect them, this number becomes four or five times as great as before, and that it is not further increased by a greater increase of density; although, like the distance to which the force of cohesion itself extends, it may be liable to some modification from the

effects of a change of temperature. Thus it is probable that the number of particles co-operating, both in repulsion and in cohesion, is diminished by the effect of heat; for the diminution of the elasticity of a spring is much more than proportional to the expansion of its substance, although the primitive repulsive force of the single particles may very possibly be as much augmented by an elevation of temperature in this case as in that of an elastic fluid: the cohesive powers of liquids are also diminished by heat, and indeed in a considerably greater degree than the stiffness of springs, although there can be no doubt that there is a considerable analogy in these changes. However this may be, it appears that the force of cohesion cannot be supposed to vary much with the density, and it is therefore allowable to consider it as constant, at all distances, as far as its action extends; while that of repulsion, though it may operate in some degree at distances somewhat greater, may still be considered, on account of its greater intensity at smaller distances, as equivalent to a resistance terminating at a more minute interval than that to which the action of cohesion extends.

The distance at which cohesion commences between the particles of gaseous fluids appears to depend entirely on the temperature, and for any one fluid it is generally reduced to one half by an elevation of about $100^\{\backslash circ\}$ of Fahrenheit. In whatever way the particles are caused to approach nearer than this distance to each other, they become subject to the action of this force, and rush together with violence, and with a great extrication of heat, until the increased repulsion affords a sufficient resistance to the cohesion, and the gas is converted into a liquid. Superficial observers have sometimes imagined, that liquids possessed little or no cohesion; and it has generally been supposed that their cohesive powers are far inferior to those of solids. But that all liquids are more or less cohesive, is sufficiently shown by their remaining attached, in small portions, to every substance capable of coming into intimate contact with them, in opposition to the effect of gravitation, or of any other force: and the cohesion of mercury is still more fully exemplified by the well-known experiment of a column, standing at a height much exceeding that of the barometer, when it has been brought, by strong agitation or otherwise, into perfect contact with the summit of the tube, and is then raised into a vertical position; the summit of the tube supporting, or rather suspending the upper parts, and each stratum the stratum immediately below it, with a force determined by the excess of its height above that of the column equivalent to the atmospheric pressure. The perfect equality of the cohesion of a given substance in the states of solidity and liquidity, appears, however, only to have been asserted in very modern times: and the assertion has only been confirmed by a single observation of the sound produced by a piece of ice, compared with the elasticity exhibited in Canton's experiments on the compressibility of water; the results demonstrating that the resistance is either accurately or very nearly equal in both cases.

The real criterion of solidity is the lateral adhesion, which prevents that change of internal arrange-

ment, by which a fluid can alter its external dimensions without any sensible difference in the mutual distances of its particles taken collectively, and consequently without any sensible resistance from the force of cohesion. It is probable that this lateral adhesion depends upon some symmetrical arrangement of the constituent parts of the substance, while fluidity requires a total independence of these particles, and an irregularity of situation, affording a facility of sliding over each other with little or no friction. The symmetry of arrangement, when continued uniformly to a sensible extent, is readily discoverable by the appearance of crystallization; but there are several reasons for supposing it to exist, though with perpetual interruptions, in more uniform masses, or in amorphous solids. It is obvious that the lateral adhesion, confining the particles so as to prevent their sliding away, performs an office like that of the tube of a barometer to which the mercury adheres, or like that of the vessels employed by Canton and Zimmerman for confining water which is compressed; and enables the cohesive and repulsive powers of the substances to be exhibited in their full extent. Nor can we obtain any direct estimate of these powers from the slight cohesion exhibited, in some circumstances, by liquids in contact with the surface of a solid which is gradually raised, and carries with it a certain portion of the liquid; an experiment which had been often made, with a view of determining the mutual attractions of solids and fluids, but which was first correctly explained, as Laplace observes, by our countryman Dr Thomas Young, from its analogy with the phenomena of capillary tubes.

There are however still some difficulties in deducing these phenomena from the elementary actions of the forces concerned, whatever suppositions we may make respecting their primitive nature. The intermediate general principle of a hydrostatic force or pressure, proportional to the curvature of the surface, had been employed long ago by Segner, and had been considered by him as the result of corpuscular powers extending to an insensible distance only. But Segner's reasoning on this point is by no means conclusive, and he has very unaccountably committed a great error, in neglecting the consideration of the effects of a double curvature. There is also an oversight in some of the steps of the demonstration attempted by Dr Young in his Lectures, which has been pointed out by an anonymous writer in Nicholson's Journal: and Mr Laplace's final equation for determining the angle of contact of a solid and a liquid, which Dr Young had first shown to be constant, has been considered as completely inaccurate, and as involving an impossibility so manifest, as to destroy all confidence in the theory from which it was deduced. A demonstration, which appears to be less exceptionable, was lately published in the Philosophical Magazine; and it may serve, with some farther illustrations, for the present purpose.

It is only necessary to consider the actions of such of the particles of the liquid, as are situated at a distance from the surface shorter than that, to which the cohesive force extends; for all those, which are more internal, must be urged equally in all di-

Cohesion. rections by the actions of the surrounding particles. Now it will readily be perceived, that the first or outermost stratum of particles will cohere very weakly with the stratum below it, having only its own attraction to bind it down; that the second will be urged by a force nearly twice as great; and that the cohesion will gradually augment, by increments continually diminishing, until we arrive at the depth of the whole interval to which the force extends: and below this it will remain constant, the number of particles within the given distance not undergoing any farther change. It has been observed by Mr Laplace, that this partial diminution of the density of the surface is likely to be concerned in facilitating the process of evaporation; and it has been cursorily suggested in another quarter, that the polarisation of light by oblique reflection may be in some measure influenced by this gradation of density. But its more immediate effect must be to produce that uniform tension of the surface, which constitutes so important a principle in the phenomena of capillary action; for since the cohesion in the direction of the surface is the undiminished result of the attractions of the whole number of particles constituting the stratum, acting as they would do in any other part of the substance, it follows that a small cubical portion of the liquid, situated in any part of the space which we are considering, will be pressed laterally by the whole force of cohesion, but above and below by that part only, which is derived from the action of the strata above it; so that this minute portion must necessarily tend to extend itself upwards and downwards, and to thicken the superficial film; and at the same time to become thinner in the direction of the surface, and to shorten it in all its dimensions; unless this alteration be prevented by some equivalent tension acting in a contrary direction: and this tension must be always the same in the same liquid, whatever its form may be, the thickness of the whole stratum being always extremely minute in comparison with any sensible radius of curvature.

Upon these grounds we may proceed to determine the actual magnitude of the contractile force derived from a given cohesion extending to a given distance. Supposing the corpuscular attraction equable throughout the whole sphere of its action, the aggregate cohesion of the successive parts of the stratum will be represented by the ordinates of a parabolic curve: for at any distance $x$ from the surface, the whole interval being $a$, the fluxion of the force will be as $dx(a-x)$, since a number of particles proportional to $dx$ will be drawn downwards by a number proportional to $a$, and upwards by a number proportional to $x$, and the whole cohesion, at the given point, will be expressed by $ax\; -\; \backslash frac\{1\}\{2\}x^2$: and this at last becomes $\backslash frac\{1\}\{2\}a^2$, which must be equal to the undiminished cohesion in the direction of the surface: consequently the difference of the forces acting on the sides of the elementary cube will everywhere be as $\backslash frac\{1\}\{2\}a^2\; -\; ax\; +\; \backslash frac\{1\}\{2\}x^2$, and the fluxion of the whole contractile force will be $dx(\backslash frac\{1\}\{2\}a^2\; -\; ax\; +\; \backslash frac\{1\}\{2\}x^2)$, the fluent of which, when $x=a$, becomes $\backslash frac\{1\}\{2\}a^3$, which is one-third of $a\; \backslash times\; \backslash frac\{1\}\{2\}a^2$, the whole undiminished cohesion of the stratum.

We may therefore conclude in general, that the contractile force is one-third of the whole cohesive

Cohesion. force of a stratum of particles, equal in thickness to the interval, to which the primitive equable cohesion extends; and if the cohesive force be not equable, we may take the interval which represents its mean extent, as affording a result almost equally accurate. In the case of water, the tension of each inch of the surface is somewhat less than three grains: consequently we may consider the whole cohesive and repulsive force of the superficial stratum as equal to about nine grains. Now since there is reason to suppose the corpuscular forces of a section of a square inch of water to be equivalent to the weight of a column about 750,000 feet high, at least if we allow the cohesion to be independent of the density, their magnitude will be expressed by $252.5\; \backslash times\; 750,000\; \backslash times\; 12$ grains, which is to 9 as $252.5\; \backslash times\; 1000,000$ to 1: consequently the extent of the cohesive force must be limited to about the 250 millionth of an inch: nor is it very probable that any error in the suppositions adopted can possibly have so far invalidated this result, as to have made it very many times greater or less than the truth.

Within similar limits of uncertainty, we may obtain something like a conjectural estimate of the mutual distance of the particles of vapours, and even of the actual magnitude of the elementary atoms of liquids, as supposed to be nearly in contact with each other: for if the distance, at which the force of cohesion begins, is constant at the same temperature, and if the particles of steam are condensed when they approach within this distance, it follows that at $60^\backslash circ$ of Fahrenheit the distance of the particles of pure aqueous vapour is about the 250 millionth of an inch: and since the density of this vapour is about one-sixty thousandth of that of water, the distance of the particles must be about forty times as great: consequently the mutual distance of the particles of water must be about the ten thousandth millionth of an inch. It is true that the result of this calculation will differ considerably according to the temperature of the substances compared; for the phenomena of capillary action, which depend on the superficial tension, vary much less with the temperature than the density of vapour at the point of precipitation: thus an elevation of temperature, amounting to a degree of Fahrenheit, lessens the force of elasticity about one ten-thousandth, the superficial tension about one thousandth, and the distance of the particles at the point of deposition about a hundredth. This discordance does not, however, wholly invalidate the general tenor of the conclusion; nor will the diversity resulting from it be greater than that of the actual measurements of many minute objects, as reported by different observers; for example those of the red particles of blood, the diameter of which may be considered as about two million times as great as that of the elementary particles of water, so that each would contain eight or ten trillions of particles of water, at the utmost. If we supposed the excess of the repulsive force of liquids above that of elastic fluids to depend rather on a variation of the law of the force than of the number of particles cooperating with each other, the extent of the force of cohesion would only be reduced to about two-thirds; and on the whole it appears tolerably safe to conclude, that, whatever errors may have affected the determi-

nation, the diameter or distance of the particles of water is between the two thousand and the ten thousand millionth of an inch.

SECTION II.—Relations of Heterogeneous Substances.

We must now return from this conjectural digression to the regions of strict mathematical argument, and inquire into the effect of the contact of substances of different kinds on the tension of their common surfaces, and on the conditions required for their equilibrium. Whatever doubts there may be respecting the variation of the number of particles cooperating when the actual density of the substance is changed, there can be none respecting the consequence of the contact of two similar substances of different densities; for the less dense must necessarily neutralise the effects of an equivalent portion of the particles of the more dense, so as to prevent their being concerned in producing any contractility in the common surface: and the remainder, acting at the same interval as when the substance remained single, must obviously produce an effect proportional to the square of the number of particles concerned; that is, of the difference of the densities of the substances. This effect may be experimentally illustrated by introducing a minute quantity of oil on the surface of the water contained in a capillary tube; the joint elevation, instead of being increased, as it ought to be according to Mr Laplace, is very conspicuously diminished: and it is obvious that since the capillary powers are represented by the squares of the density of oil and of its difference from that of water, their sum must be less than the capillary power of water, which is proportional to the square of the sum of the separate quantities.

Upon these principles, we may determine the conditions of equilibrium of several different substances meeting in the same point, neglecting for a moment the consideration of solidity or fluidity, as well as that of gravitation, in estimating the contractile powers of the surfaces and their angular situations. We suppose then three liquids, of which the densities are $A$, $B$, and $C$, to meet in a line situated in the plane termination of the first: the contractile forces of the surfaces will then be expressed by $(A-B)^2$, $(A-C)^2$, and $(B-C)^2$: and if these liquids be so arranged as to hold each other in equilibrium, whether with or without the assistance of any external force, the equilibrium will not be destroyed by the congelation of the first of the liquids, so that it may constitute a solid. Now, unless the joint surface of the second and third coincides in direction with that of the first, it cannot be held in equilibrium by the contractility of this surface alone; but supposing these two forces to be so combined, as to produce a result perpendicular to the surface of the first substance, this force may be resisted by its direct attraction; the forces which tend to cause the oblique surface to move either way on it, balancing each other, and the perpendicular attraction being counteracted by some external force holding the solid in its situation. Consequently the force expressed by $(B-C)^2$, reduced in the proportion of the radius to the cosine of the angle, must become equal to the difference of

the forces $(A-B)^2$ and $(A-C)^2$, and if the radius be called unity, this cosine must be $\backslash frac\{(A-C)^2\; -\; (A-B)^2\}\{(B-C)^2\}\; =$

the excess of twice the density of the solid above the sum of the densities of the liquids, divided by the difference of these densities: and when there is only one liquid, and $C=0$, this cosine becomes $\backslash frac\{2A\}\{B\}\; -\; 1$, vanishing when $2A=B$, and the density

of the solid is half of that of the liquid, the angle then becoming a right one, as Clairaut long ago inferred from other considerations. Supposing the attractive density of the solid to be very small, the cosine will approach to $-1$, and the angle of the liquid to two right angles: and on the other hand, when $A$ becomes equal to $B$, the cosine will be $1$, and the angle will be evanescent, the surface of the liquid coinciding in direction with that of the solid. If the density $A$ be still further increased, the angle cannot undergo any further alteration, and the excess of force will only tend to spread the liquid more rapidly on the solid, so that a thin film would always be found on its surface, unless it were removed by evaporation, or unless its formation were prevented by some unknown circumstance which seems to lessen the intimate nature of the contact of liquids with dry solids. For the case of glass and

mercury, we find $\backslash frac\{A\}\{B\}$ about $\backslash frac\{1\}\{2\}$, and the cosine $-\backslash frac\{3\}\{4\}$,

which corresponds to an angle of $139^\backslash circ$: and if we add a second liquid, the expression will become

than $180^\backslash circ$, as long as $C$ remains less than $1$, or as long as the liquid added is less dense than glass. There must, therefore, have been a slight inaccuracy in the observation mentioned by Mr Laplace, that the surface of mercury contained in a glass tube becomes hemispherical under water: and if we could obtain an exact measurement of the angle assumed by the mercury under these circumstances, we should at once be able to infer from it the comparative attractive density of water and glass, which has not yet been ascertained; although it might be deduced with equal ease from the comparative height of a portion of mercury, contained in two unequal branches of the same tube, observed in the air and under water. The cosine is more exactly $-.735$, in the case of the contact of glass and mercury, and

portion somewhat greater than that of the specific gravities; but it must probably vary with the various kinds of glass employed.

There is also another mode of determining the angle of contact of a solid with a single liquid, which has been ingeniously suggested by Mr Laplace; it is derived from the principle of the invari-

Cohesion. ability of the curvature of the surface at a given elevation; and its results agree with those which we have already obtained, except that it does not appear to be applicable to the case of more than one liquid in contact with the given solid. Supposing a capillary tube to be partially inserted into a liquid, if we imagine it to be continued into a similar tube of the liquid, leaving a cylinder or column of indefinite length in the common cavity; then the action of either tube, upon the liquid immediately within it, will have no tendency either to elevate or to depress the column: but the attraction of the portion of the tube above the column will tend to raise it with a certain force, and the lower end of the tube will exert an equal force upon the portion of the column immediately below it; and this double force will only be opposed by the single attraction of the liquid continuation of the tube, drawing down the column above it, so that the weight of the column suspended will be as the excess of twice the attractive force of the solid above that of the liquid. Now supposing two plates of the solid in question to approach very near each other, so that the elevation may be very great in comparison with the radius of curvature of the surface, which in this case may be considered as uniform; the weight suspended will then be simply as the elevation, which will be the measure of the efficient attractive force, and will vary with it, if we suppose the nature of the solid to vary, the radius of curvature varying in the inverse ratio of the elevation: but the radius of curvature is to half the distance of the plates, as unity to the numerical sine of half the angular extent of the surface, or the cosine of the angle of the liquid, so that this cosine will be inversely as the radius, or directly as the elevation; that is, as the efficient attractive force, which is expressed by $2A\; -\; B$, becoming $=\; -1$ when $A$ vanishes, and consequently being always

equal to $\backslash frac\{2A\; -\; B\}\{B\}$, as we have already found from

other considerations. If we wished to extend this mode of reasoning to the effect of a repulsive force counteracting the cohesion, we should only have to suppose the diameter of the tube diminished on each side by the interval which is the limit of the repulsion, since beyond this the repulsion could not interfere with the truth of the conclusions, for want of any particles situated in the given directions near enough to each other to exhibit it: and within the stratum more immediately in contact with the solid, the forces may be supposed to balance each other by continuing their action along its surface until they are opposed by similar forces on the outside of the tube or elsewhere: and indeed such a repulsive stratum seems in many cases to be required for affording a support to the extended surface of the liquid when the solid does not project beyond it. It may also be shown, in a manner nearly similar, by supposing the column to be divided into concentric cylinders, that the superficial curvature of the liquid will not affect the truth of the conclusion.

SECTION III.—Forms of Surfaces of Simple Curvature.

We may now proceed upon the principle, admitted

by all parties, of a hydrostatic pressure proportional to the curvature of the surface of the liquid, which is equivalent to a uniform tension of that surface, and which either supports the weight or pressure of the fluid within its concavity, or suspends an equal column from its convexity, whether with the assistance of the pressure of the atmosphere, or more simply, by the immediate effect of the same cohesion, that is capable of retaining the mercury of the barometer in contact with the summit of the tube: and on this foundation, we may investigate the properties of the forms assumed by the surface; first considering the cases of simple curvature, which are analogous to some of the varieties of the elastic curve, and next those of the surfaces having an axis of revolution, which will necessarily involve us in still more complicated calculations.

A. Let the height of the curve at its origin be $a$, the horizontal absciss $x$, the vertical ordinate $y$, the sine of the angular elevation of the surface $s$, the versed sine $v$, and the rectangle contained by the ordinate and the radius of simple curvature $r$; then the area of the curve will be $rs$, and $y\; =\; \backslash sqrt\{a^2\; +\; 2rv\}$.

The fluxion of the curve $z$ is jointly as the radius of curvature $\backslash frac\{r\}\{y\}$, and as the fluxion of the angle of

elevation, which we may call $\backslash omega$, or $dz\; =\; \backslash frac\{r\}\{y\}\; d\backslash omega$, and

$d\backslash omega\; =\; ds$, consequently $dz\; =\; \backslash frac\{r\}\{y\}\; ds$, and $y\; dx$, the

fluxion of the area, becomes equal to $rd\; s$, and the area itself to $rs$. In order to find $y$, we have $dy\; =$

$2rv\; +\; aa$, $y$ becoming equal to $a$ when $v$ vanishes.

It may also be immediately inferred, that the area of the curve must vary as the sine of the inclination of the surface, from considering that, according to the principles of the resolution of forces, the tension being uniform, the weight which it supports must be proportional to that sine.

Scholium. The value of $r$ for water at common temperatures, is about one hundredth of a square inch, according to the results of a variety of experiments compared by Dr Young; or more correctly, if we adopt the more recent measurement of Mr Gay-Lussac, .0115: for alcohol Mr Gay-Lussac's experiments give $r\; =\; .0047$; and for mercury $r\; =\; .0051$. Dr Young had employed .005 for mercury, a number which appears to be so near the truth, that it may still be retained for the greater convenience of calculation. Hence in a very wide vessel, the smallest ordinate $a$ being supposed evanescent, and $y\; =\; \backslash sqrt\{(2rv)\}\; =\; .1516\; \backslash sqrt\{v\}$, the height of the water rising against the side of the vessel, when $v\; =\; 1$, will be .1516; and the utmost height at which the water will adhere to a horizontal surface, raised above its general level, will be $2\backslash sqrt\{r\}\; =\; .2145$. For mercury, $y$ becomes, in these circumstances, $\backslash sqrt\{(.0102v)\}\; =$

Cohesion. .101 $\backslash sqrt\{v\}$, and if $s\; =\; .735$, $v\; =\; .322$, and the depression of the surface in contact with a vertical surface of glass becomes .0573; and again when $v\; =\; 1.735$, as in the case of a large portion of mercury lying on a plate of glass, the height $y$ is .133: and if the glass had no attraction at all for mercury, $v$ would become 2, and the height .1428. The actual tension of the surface of mercury is to that of water as $.0051\; \backslash times\; 13.6$ or $.06936$ to $.0115$; that is a little more than six times as great; while the angle of contact of mercury with glass, which is more attractive than water, would have led us to expect a disproportion somewhat greater. If we take a mean of these results, and estimate it at seven times, the value of $\backslash sqrt\{r\}$ will be reduced, by immersing mercury standing on

glass into water, in the ratio of $\backslash frac\{6\}\{7\}\; \backslash times\; \backslash sqrt\{\backslash frac\{13.6\}\{12.6\}\}$, since

the buoyant effect of the water increases the value of $r$, so that $\backslash sqrt\{(2r)\}$ will be .09; and the angle approaching to $180^\backslash circ$, the height will be about .127.

B. When the curve is infinite the absciss $x$ becomes $=\; \backslash frac\{1\}\{2\}\; \backslash sqrt\{r\}\; \backslash text\{\; HL\}\; \backslash frac\{2\backslash sqrt\{r\}\; -\; \backslash sqrt\{(4r\; -\; yy)\}\}\{2\backslash sqrt\{r\}\; +\; \backslash sqrt\{(4r\; -\; yy)\}\}\; +\; \backslash sqrt\{(4r\; -\; y^2)\}$, reckoning from the greatest ordinate $y\; =\; 2\backslash sqrt\{r\}$; and the excess of the length of the curve above the absciss is $2\backslash sqrt\{r\}\; -\; \backslash sqrt\{(4r\; -\; y^2)\}$.

In this case, $a$ being $=\; 0$, $y^2\; =\; 2rv$; but $\backslash frac\{dx\}\{dy\}\; =\; \backslash frac\{1-v\}\{s\}\; =\; \backslash frac\{1-v\}\{\backslash sqrt\{(2v-vv)\}\}\; =\; \backslash frac\{2r-2rv\}\{\backslash sqrt\{(4r-2rv)\backslash sqrt\{(2rv)\}\}\}\; =\; \backslash frac\{2r-yy\}\{\backslash sqrt\{(4r-yy)y\}\}$; and, by the common rules for finding fluents, $x\; =\; \backslash frac\{2r\}\{4\backslash sqrt\{r\}\}\; \backslash text\{\; HL\}\; \backslash frac\{2\backslash sqrt\{r\}\; -\; \backslash sqrt\{(4r\; -\; yy)\}\}\{2\backslash sqrt\{r\}\; +\; \backslash sqrt\{(4r\; -\; yy)\}\}\; +\; \backslash sqrt\{(4r\; -\; y^2)\}$; which vanishes when $y\; =\; 2\backslash sqrt\{r\}$: and for the length of the curve, since $\backslash frac\{dz\}\{dy\}\; =\; \backslash frac\{1\}\{s\}\; =\; \backslash frac\{1\}\{\backslash sqrt\{(2v-vv)\}\}$, subtracting the former

fluxional coefficient from this, we have $\backslash frac\{y\; dy\}\{\backslash sqrt\{(4r\; -\; yy)\}\}$ for the fluxion of the difference; and the fluent of this is $=\; \backslash sqrt\{(4r\; -\; y^2)\}$.

Corollary 1. Hence, where the curve is vertical, we find $x\; =\; .5328\; \backslash sqrt\{r\}$: and where the inclination amounts to a second, $x\; =\; 11.28\; \backslash sqrt\{r\}$; for example, in the case of water, $\backslash sqrt\{r\}$ being .1072, the latter value of $x$ will become 1.21, and the former .056: so that the surface must be considered as sensibly inclined to the horizon at the distance of more than an inch from the vessel, but scarcely at an inch and a half: and for mercury, these distances will be two-thirds as great. This circumstance must not be forgotten when mercury is employed for an artificial horizon; although, where the vessel is circular, the surface becomes horizontal at its centre; and in other parts

the inclination is materially affected by the double curvature.

Corollary 2. The form of the surface coincides in this case with that of an elastic bar, or a slender spring, of infinite length, supposed to be bent by a weight fixed to its extremity; since the curvature of such a spring must always be proportional to its distance from the vertical line passing through the weight. We may therefore deduce from this proposition the correction required for the length of a pendulum like Mr Whitehurst's, consisting of a heavy ball, suspended by a very fine wire. Now the radius

of curvature of the spring is $\backslash frac\{Maa\}\{12fy\}$ (Art. BRIDGE,

Prop. G); the modulus of elasticity, of which $M$ is the weight, being for iron or steel about 10,000,000 feet in height; and since 80 inches of the wire weighed 3 grains, the thickness $a$, supposing it to have been $\backslash frac\{1\}\{3\}$ or $\backslash frac\{2\}\{3\}$ of the breadth, as is usual in wire flattened for hair springs, must have been about $\backslash frac\{1\}\{3\}$ of an inch: the weight $f$ was 12251 grains: and the

weight $M$ of ten million feet must have been $\backslash frac\{3\}\{80\}\; \backslash times$

$12\; \backslash times\; 10000000$ grains; consequently $\backslash frac\{Maa\}\{12fy\}\; =$

$\backslash frac\{3\; \backslash times\; 10000000\}\{80\; \backslash times\; 12251\; \backslash times\; 375\; \backslash times\; 375y\}\; =\; \backslash frac\{1000\}\{12251\; \backslash times\; 375y\}\; =$

$\backslash frac\{1\}\{4594y\}$, which is analogous to $\backslash frac\{r\}\{y\}$ in these propositions;

consequently $\backslash sqrt\{r\}\; =\; \backslash frac\{1\}\{2\backslash sqrt\{3\}\}$; and the whole value of $\backslash sqrt\{(4r\; -\; y^2)\}$ from $y\; =\; 2\backslash sqrt\{r\}$ to $y\; =\; 0$, is $\backslash frac\{1\}\{3\}$ of an inch. Now supposing the spring to have been firmly fixed at the axis of vibration, the excess of its length above the ordinate will always be measured by $2\backslash sqrt\{r\}\; -\; \backslash sqrt\{(4r\; -\; y^2)\}$; but $\backslash sqrt\{(4r\; -\; y^2)\}\; =\; \backslash sqrt\{(4r\; -\; 2rv)\}\; =\; \backslash sqrt\{r\}\; \backslash sqrt\{(4\; -\; 2v)\}$, which is the chord of the supplement of the arc of vibration in the circle of which the radius is $\backslash sqrt\{r\}\; =\; \backslash frac\{1\}\{2\backslash sqrt\{3\}\}$; and the ball will be drawn above its path to a height equal to the distance between this circle and another of twice the diameter, touching it at its lowest point: but a perpendicular falling from this point on the wire would always be found in a circle twice as much curved as the first circle, and if it were made the centre of vibration, the ball would always be raised twice as far above its original path as the distance between the first circle and the second, which is the measure of the effect of the curvature; so that the pendulum must be supposed to be shortened half as much as this; that is, in the present instance, $\backslash frac\{1\}\{3\}$ of an inch: If however the spring remained in Mr Whitehurst's experiments, at liberty to turn within the clip, and was firmly fixed at a considerable distance above, the variation of the length must have been only that which belongs to half of the arc of vibration; that is, one fourth as great as in the former case, since the versed sine is initially as the square of the arc; but since it would affect the spring both above and below the clip, it would be doubled from this cause, and would amount to $\backslash frac\{1\}\{3\}$ of an inch: so that the true correction would be liable to vary from .00735 to .00367, according

to the mode of fixing the wire. But since this error must have affected both Mr Whitehurst's pendulums in an equal degree, and the result was deduced from the difference, and not the proportion of the lengths, it is free from any inaccuracy on this account. The calculation however sufficiently proves the necessity of attending to the effect of different modes of fixing the spring, in order that no variation may be made in the different experiments compared without a proper correction. The elasticity of such a wire, as Mr Whitehurst employed, could not have produced any sensible error, by co-operating with the force of gravitation, since it did not amount to one two-millionth part of the weight of the ball.

C. The relation of the ordinate and absciss may be generally expressed by means of an infinite series.

When the curve is concave towards the absciss throughout its extent, the ordinate may be compared with the lengths of hyperbolic and elliptic arcs, as Maclaurin has shown with respect to the elastic curve (Fluxions, § 928): but his solution fails in the more ordinary cases of the problem; and even where it is applicable, the calculation is very little facilitated by it. Segner has made use of two different forms of infinite series, each having its peculiar advantages with respect to convergence in particular cases, and other forms may be found, which will sometimes be more convenient than either of these.

The value of the cotangent $\backslash frac\{dx\}\{dy\}$ being in general

$\backslash frac\{2r-yy+aa\}\{\backslash sqrt\{(4r-yy+aa)\}\}\; \backslash cdot\; \backslash frac\{1\}\{\backslash sqrt\{(yy-aa)\}\}$, we may retain either of these fractions, and expand the other by means of the binomial theorem.

1. In the first place, making $4r+a^2=c^2$, we have $(c^2-y^2)^\{-\backslash frac\{1\}\{2\}\}\; =\; \backslash frac\{1\}\{c\}\; +\; \backslash frac\{1\}\{2\}\; \backslash cdot\; \backslash frac\{y^2\}\{c^3\}\; +\; \backslash frac\{3\}\{4\; \backslash cdot\; 2\}\; \backslash cdot\; \backslash frac\{y^4\}\{c^5\}\; +\; \backslash frac\{5\}\{8\; \backslash cdot\; 2\; \backslash cdot\; 3\}\; \backslash cdot\; \backslash frac\{y^6\}\{c^7\}\; +\; \backslash dots$, and $\backslash frac\{dx\}\{dy\}\; =\; \backslash frac\{2r+aa\}\{\backslash sqrt\{(yy-aa)\}\}$

Now, in order to find the fluents of the separate terms, we have first $\backslash int\; \backslash frac\{dy\}\{\backslash sqrt\{(yy-aa)\}\}\; =\; \backslash text\{HL\}\; (y\; +\; \backslash sqrt\{[yy-aa]\})$; and calling this logarithm L,

2. If we reduce $\backslash frac\{1\}\{\backslash sqrt\{(yy-aa)\}\}$ into a series, we have $\backslash left(1\; -\; \backslash frac\{aa\}\{yy\}\backslash right)^\{-\backslash frac\{1\}\{2\}\}\; =\; 1\; +\; \backslash frac\{1\}\{2\}\; \backslash cdot\; \backslash frac\{a^2\}\{y^2\}\; +\; \backslash frac\{3\}\{4\; \backslash cdot\; 2\}\; \backslash cdot\; \backslash frac\{a^4\}\{y^4\}\; +\; \backslash frac\{5\}\{8\; \backslash cdot\; 2\; \backslash cdot\; 3\}\; \backslash cdot\; \backslash frac\{a^6\}\{y^6\}\; +\; \backslash dots$, and $\backslash frac\{dx\}\{dy\}\; =\; \backslash frac\{2r+aa-yy\}\{\backslash sqrt\{(cc-yy)\}\}$. $\backslash left(\; \backslash frac\{1\}\{y\}\; +\; \backslash frac\{1\}\{2\}\; \backslash cdot\; \backslash frac\{a^2\}\{y^3\}\; +\; \backslash frac\{3\}\{4\; \backslash cdot\; 2\}\; \backslash cdot\; \backslash frac\{a^4\}\{y^5\}\; +\; \backslash dots\; \backslash right)$. Then, for the fluents,

3. These series may be employed with advantage where the initial ordinate is very small, the one being more convenient for the upper, and the other for the lower part of the curve: but where the elevation $a$ is more considerable, the form of the curve will be more readily determined by means of fluents derived from circular arcs. Beginning with the expressions $\backslash frac\{dx\}\{dy\}\; =\; \backslash frac\{1-v\}\{\backslash sqrt\{(2v-vv)\}\}$, and $y^2\; =\; a^2\; +\; 2rv$, we may seek for a value of $x$ in terms of $v$; and since $2ydy\; =\; 2r\; dv$, $dy\; =\; \backslash frac\{r\}\{y\}\; dv\; =\; \backslash frac\{r\; dv\}\{\backslash sqrt\{(aa+2rv)\}\}$, and $dx\; =$

Cohesion. of which $v$ is the versed sine; $\backslash int\; \backslash frac\{v\; dv\}\{s\}\; =\; s\; -\; w$; $\backslash int\; \backslash frac\{v^2\; dv\}\{s\}\; =$

4. Another series may be obtained by the expansion of $\backslash sqrt\{\backslash frac\{1\}\{(2v-vv)\}\}$ into $\backslash sqrt\{\backslash frac\{1\}\{(2v)\}\}$.

fluxions belonging to the series $(y^2\; -\; a^2)\; -\; \backslash frac\{1\}\{2\}dy$, $(y^2\; -\; a^2)^\{\backslash frac\{1\}\{2\}\}\; dy$, $(y^2\; -\; a^2)^\{\backslash frac\{3\}\{2\}\}\; dy$; and the fluents of these are $HL(y\; +\; \backslash sqrt\{[y^2\; -\; a^2]\})\; =\; L$; $\backslash frac\{1\}\{2\}y\; \backslash sqrt\{(y^2\; -\; a^2)\}\; -\; \backslash frac\{1\}\{2\}a^2\; L$; $(\backslash frac\{1\}\{2\}\; \backslash sqrt\{(y^2\; -\; a^2)\}\; +\; \backslash frac\{3\}\{8\}a^2)\; y\; \backslash sqrt\{(y^2\; -\; a^2)\}\; +\; \backslash frac\{3a^4\}\{8\}\; L$; which afford a result somewhat resembling that which is deduced from the first method.

5. We may also express $x$ in a series of integral powers of $y$ only, if we suppose it to begin at some point in which the curve is inclined to the horizon, where the height is $p$, calling it at other points $p+y$;

and making $\backslash frac\{dx\}\{dy\}\; =\; r\; =\; a\; +\; by\; +\; cy^2\; +\; \backslash dots$; we have then $x\; =\; \backslash beta\; +\; ay\; +\; \backslash frac\{1\}\{2\}by^2\; +\; \backslash frac\{1\}\{2\}cy^3\; +\; \backslash dots$, and the area $\backslash int\; (p+y)\; dx\; =\; \backslash gamma\; +\; pay\; +\; \backslash frac\{1\}\{2\}pby^2\; +\; \backslash dots\; +\; \backslash frac\{1\}\{2\}ay^2\; +\; \backslash frac\{1\}\{2.3\}by^3\; +\; \backslash frac\{1\}\{3.4\}cy^4\; +\; \backslash dots$, which must be equal to $rs$

(Prop. A.): but $s\; =\; \backslash sqrt\{\backslash frac\{dy\}\{(dx^2\; +\; dy^2)\}\}\; =\; \backslash sqrt\{\backslash frac\{1\}\{(1+r^2)\}\}$, which

may be developed by means of the Taylorian theorem

taking $A\; =\; a$, and $H\; =\; by\; +\; cy^2\; +\; \backslash dots$, whence

$pay\; +\; (\backslash frac\{1\}\{2\}pb\; +\; \backslash frac\{1\}\{2\}a)y^2\; +\; (\backslash frac\{1\}\{2\}pc\; +\; \backslash frac\{1\}\{2\}b)y^3\; +\; \backslash dots$; and hence by comparing the homologous terms, we find $\backslash gamma\; =\; \backslash frac\{r\}\{\backslash sqrt\{(1+aa)\}\}$,

6. We may still more readily obtain a similar series for $y$ in terms of the powers of $x$ with constant coefficients; calling $\backslash frac\{dy\}\{dx\}\; =\; t$, and making $t\; =\; bx\; +\; cx^2\; +\; dx^3\; +\; \backslash dots$ whence $y\; =\; a\; +\; \backslash frac\{1\}\{2\}bx^2\; +\; \backslash frac\{1\}\{2\}cx^3\; +\; \backslash frac\{1\}\{2\}dx^4\; +\; \backslash dots$, and the area $\backslash int\; y\; dx\; =\; ax\; +\; \backslash frac\{1\}\{2.3\}bx^3\; +\; \backslash frac\{1\}\{4.5\}cx^5\; +\; \backslash dots\; =\; rs\; =\; \backslash sqrt\{\backslash frac\{rt\}\{(1+tt)\}\}\; =\; rt\; (1\; -\; \backslash frac\{1\}\{2\}t^2\; +\; \backslash frac\{3\}\{4.2\}t^4\; -\; \backslash frac\{3.5\}\{8.2.3\}t^6\; +\; \backslash dots)$. But $t^2\; =\; b^2x^2\; +\; 3b^2cx^3\; +\; \backslash dots$ and $t^3\; =\; b^3x^3\; +\; \backslash dots$; hence we have the equation

It is the less necessary to enter into any further detail of these results, as we have a table, calculated by Segner, with his son's assistance, which is sufficient to afford us a general idea of the forms of the curve in different circumstances. The unit of this table is the quantity $\backslash sqrt\{r\}$, which Segner calls the modulus of capillary attraction, and which for water is .1072 inch. The table begins with the extreme ordinate, where the curve is vertical: we have then the least ordinate, $a$; the greatest ordinate, where the curve again becomes horizontal, and the abscissa corresponding to the extreme ordinate and to the greatest ordinate.

It may be observed that the last six values of the least ordinate are in geometrical progression, while the absciss increases in arithmetical progression; the difference of the absciss 2.3, being the hyperbolic logarithm of 10, which is the common multiplier of the ordinates. Although the table appears to be generally accurate, yet we cannot always depend on the last figures: thus the ultimate difference of the two last columns is made .43, while it ought to be .53 (Prop. B. Cor. 1). It is scarcely necessary to remark, that if we look, in the fourth column, for half the distance between two parallel planes of glass, in a vertical position, the first and second columns will give us the height to which water will rise between them, where it touches the glass, and in the middle of the interval.

When the liquid is contained in a tube, or when it forms itself spontaneously into a drop having an axis of revolution, it becomes necessary to consider the effect of the tension in a direction transverse to that of the principal section; since the curvature

will cause it to exhibit an equal pressure, whatever the direction of the section to which it belongs may be; and the curvatures of the sections perpendicular to each other will either cooperate with, or counteract each other, accordingly as the convexities of both are on the same side, or on the opposite sides, of the surface. But the simple consideration of the tension, supporting the weight of the parts below, or the equivalent pressure in a contrary direction, will at once afford us the equations necessary for the solution of the problem, without any immediate reference to the curvature in question.

D. The form of a surface of revolution may be determined by means of an infinite series.

The fluxion of the weight or mass of the parts, contained within the cylindrical surface, of which $x$ is the radius or absciss, and $y$ the ordinate, being always proportional to $yxdx$, and the fluent to $\backslash int\; yxdx$; and the extent of the circumference supporting it varying also as $x$, and the contractile force being diminished, when reduced to the direction of gravitation, in the ratio of the radius unity to the sine of the elevation $s$, it will always be proportional to $xs$; so that we have the general equation $\backslash int\; yxdx\; =\; mxs$. Now if we suppose $y$ incomparably greater than $x$, and the surface extremely minute, the variation of $y$ may be neglected, and we have in this case $\backslash int\; yxdx\; =\; \backslash frac\{1\}\{2\}yx^2$; and supposing also $s\; =\; 1$, and the curve vertical, $\backslash frac\{1\}\{2\}yx^2\; =\; mx$, and $\backslash frac\{1\}\{2\}yx\; =\; m$; $x$ becoming also equal to the radius of curvature: but it is easy to perceive that the height $y$ must be twice as great, for any value of $x$, as in the case of a simple curvature, since each portion of the circumference has here only to support a wedge, which is only half as heavy as a parallelepiped of the same height; so that $\backslash frac\{1\}\{2\}yx$ will be equal to $yx$ in Proposition A, and $m\; =\; r$.

In order to obtain a series for finding $y$, from the equation $\backslash int\; yxdx\; =\; mxs$, we may put the tangent

Proposition C. n 6, calling $\backslash frac\{1\}\{m\}$, or $\backslash frac\{1\}\{r\}$, $q$, we find $s\; =$

consequently $b\; =\; \backslash frac\{1\}\{2\}qa\; =\; \backslash frac\{a\}\{2r\}$, and $a\; =\; \backslash frac\{2b\}\{q\}\; =\; 2rb$, and

Cohesion. by continuing the calculation and reducing the values, we find

We may here observe, that the numerical coefficients of the highest powers of $b$ form the series $\backslash frac\{1\}\{2\}$,

$\backslash frac\{3\}\{2.4\}\; \backslash cdot\; \backslash frac\{3.5\}\{2.4.6\}\; \backslash cdot\; \backslash frac\{3.5.7\}\{2.4.6.8\}\; \backslash cdot\; \backslash frac\{6\}\{2.4.6.8.10\}\; \backslash cdot\; \backslash frac\{3.5.7.9\}\{2.4.6.8.10\}\; \backslash cdot\; \backslash frac\{8\}\{6\}$, the ratio of the

successive terms of both continually approaching to equality; and those of the next in order the

series $\backslash frac\{3\}\{2.4\}\; \backslash cdot\; \backslash frac\{2\}\{6\}\; \backslash cdot\; \backslash frac\{3.5\}\{2.4.6\}\; \backslash cdot\; \backslash frac\{4\}\{6\}\; \backslash cdot\; \backslash frac\{3.5.7\}\{2.4.6.8\}$; but the laws of the

numerical coefficients in general appear to be wholly incapable of being reduced to any simple form. It will be convenient for calculation to form tables of the logarithmic values of these coefficients, which may be continued, by means of successive differences, for as many terms as are requisite for any practical purpose. The indices, with lines drawn over them, are to be considered as negative numbers.

Logarithmic Coefficients of the Value of the Sine. Cohesion.

Logarithmic Coefficients of the Value of the Ordinate y.

Cohesion. E. The elevation or depression of a liquid contained in a given tube may be found by reversing the series.

Having a given value of $x$, the semidiameter of the tube, and also of $s$, the elevation or depression of the surface of the liquid at the point of contact with the solid, we obtain an equation of the form $s\; =\; Ab\; +\; Bb^5\; +\; Cb^7\; +\; \backslash dots$, and from this we may determine the central elevation or depression $a\; =\; 2rb$ by the well known method of the reversion of series, which give us the value $b\; =\; \backslash frac\{1\}\{A\}\; s\; -\; \backslash frac\{B\}\{A^4\}\; s^3\; -$

But it is more convenient to assume an approximate

value of $b$, a little less than $\backslash frac\{s\}\{A\}$, and to find the corresponding value of $s$; then since $ds\; =\; Ad\; b\; +\; 3\; B\; b^4\; d\; b\; +\; 5\; C\; b^6\; d\; b\; +\; \backslash dots$, if we make $Ab\; +\; 3\; B\; b^4\; +\; 5\; C\; b^6\; +\; \backslash dots\; =\; \backslash Sigma$, we shall have $\backslash frac\{ds\}\{db\}\; =\; \backslash frac\{\backslash Sigma\}\{b\}$;

consequently the small increments of $s$ and $b$ will be to each other as $\backslash Sigma$ to $b$, and we obtain the correction of $b$ from the error of the calculated value of $s$: and if the calculation be repeated with the corrected value of $b$, the second result will always be sufficiently near to the truth.

In order to judge of the accuracy of this mode of calculation, which Mr Laplace appears to have thought liable to some undefined objection, it will be necessary to enter into the details of its different elements, which will sufficiently show the degree of convergence of the series, and the greatest possible amount of error.

Values of the Coefficients of $s$ for Tubes of different Diameters, $r$ being .005, and $s\; =\; .75$.

It appears upon inspection of this table, that the coefficients of $bx$ alone always determine $\backslash frac\{2\}\{3\}$ of the value of the quantity required, and these are easily calculated with perfect accuracy, so that the error must always be far less than $\backslash frac\{1\}\{10\}$, and in fact the actual uncertainty never exceeds $\backslash frac\{1\}\{100\}$ of the whole, at least in the last four examples. The differences of Mr Laplace's approximative calculations from these results are incomparably greater, so that we cannot hesitate to consider these differences as er-

Cohesion. rors. Indeed, when we recollect that in the method employed by Mr Bouvard, under Mr Laplace's directions, the radius of curvature of each of the small portions, into which the curve has been cut up, has been determined from the ordinate at the beginning of the portion, it is obvious that the curvature thus found must be less than the truth, and that in order to obtain any required curvature of the whole surface, the depression must be increased in the same proportion: and there is no ready way of appreciating the amount of this error. Dr Young had before attempted to avoid it, in making an estimate of the same nature, by calculating for the middle of each portion; but from some accident, the numbers of his table, published in 1807, are generally a little too small, although the method, which he then employed, is nearly the same as that which Mr Laplace afterwards adopted; except that for the lowest portion of the curve, Mr Laplace had recourse to an infinite series, applicable only to that part. The elements deduced in Nicholson's journal for 1809, from Mr Gay Lussac's experiments, which are $r\; =\; .0051$ and $s\; =\; .7353$, agree better with the numbers found in Mr Laplace's table, than those from which it was constructed, which were $r\; =\; .005038$ and $s\; =\; .729$; the depressions being always a little larger than the true results from the elements assumed.

The value of the ordinate $y$ depends also principally on the first variable member of the series, although the subsequent coefficients are not so inconsiderable as in the determination of the sine. Thus taking $x\; =\; .2$, and $b\; =\; 1.503$, we have $y\; =\; a\; +\; .813\; bx^2\; +\; .99\; b^3\; x^4\; +\; 2.97\; b^5\; x^6\; +\; \backslash dots\; =\; .01503\; +\; .0489\; +\; .0054\; +\; .0015\; +\; [.0006]\; =\; .0714$, which is the marginal depression, leaving .0564 for the height of the convex portion $y\; -\; a$. We may determine the effect of any small variations in this height, in the same manner as that of the sine of the inclination: supposing them to depend on a change of the angle of contact only, the quantity $r$ remaining unaltered, it is obvious that $q$ and $x$ must retain their value, while $y$ and $b$ only vary; and making

$=\; d(y-a)\; :\; db$. In the present instance, we find $Y\; =\; .0489\; +\; 3\; \backslash times\; .0054\; +\; 5\; \backslash times\; .0015\; +\; \backslash dots\; =\; .079$; and supposing, as in the example suggested by Mr Laplace, the variation of the height $y\; -\; a$ to be .00394, which is $\backslash frac\{1\}\{20\}$ of $Y$, that of $b$ will be $\backslash frac\{1\}\{20\}$ of $b$, or .075, and the variation of the central depression $a$, .00075, which is somewhat less than one fifth of the alteration in the height of the convex portion: but in smaller tubes it is obvious that the variations of the depression $a$ might much exceed that of the height of the convex portion. Nothing can be easier or more direct than this part of the calculation; and it is remarkable that Mr Laplace should have considered the awkward contrivance of building up a curve, like the arch of a bridge, with fourteen blocks on each side, as possessing any thing like an "advantage" over the series in the determination of this variation.

If we wish to find the effect of a small variation of the diameter of a tube, from $D$ to $D\; \backslash pm\; D\text{'}$, on the depression $a$ of the mercury contained in it, we may

C being about 2.9 for tubes between 1 inch and $\backslash frac\{1\}\{4\}$th of an inch in diameter, and being elsewhere easily deduced from the depressions already known. For variations of the cohesive power, and of its measure $r$, we may suppose the whole of the numbers of the table to be altered in the proportion of the supposed alteration of $\backslash sqrt\{r\}$, and the change produced by restoring the diameter to its former dimensions may then be calculated like any other interpolation. There is also a more comprehensive formula, which seems to express the depression in tubes of all sizes with great accuracy; it is this, $a\; =\; \backslash frac\{.015\}\{D\; +\; 48\; D^\{5.492\; +\; 3.20\; D\}\}$:

and it might even be possible to shorten the original calculation by a comparison of the series with the expansion of this empirical formula, if it were of any further importance to facilitate the mode of computation. But for all practical purposes, it will be sufficient to collect the results already obtained into a comparative table, arranged in chronological order; and it is remarkable, that they are all comprehended, without any material exception, between the two values assigned to each as near the truth in Dr Young's first table, the mean of those values never differing a thousandth of an inch from the result of the more correct calculation; while the error of Lord Charles Cavendish's experiments, notwithstanding their general accuracy, sometimes amounts to nearly one hundredth.

UNDER this head it will be proper to give a brief account of the constitution of the Royal Mint, as well as of the different processes which come under the general term Coinage; for all these processes are conducted under various checks emanating from the constitution which the legislature has thought proper to give this Royal Establishment.

The Royal Mint attained its constitution of superior officers in the 18th year of the reign of Edward II., and, with very few alterations, continued as then established till the year 1815. Of the alterations in this latter year we shall have occasion to speak hereafter.

Edward appointed a Master, Warden, and Comptroller, King's and Master's Assay Master, and King's Clerk, besides several inferior officers, whose duties will be mentioned hereafter. Previous to this period, we have very little information as to the system of coinage pursued at the various mints which the kings

of England had throughout their dominions. The Rev. Roger Ridding, in his valuable and laborious Annals of the Coinage of Britain and its Dependencies, gives it as his opinion, that the moneyers were in very early ages the only officers employed in the fabrication of the money. On the early Anglo-Saxon coins are found, besides the names of the monarchs, those of other persons, who are with great probability conjectured to have been the moneyers, because on the later Anglo-Saxon money the names of those officers frequently occur, with the addition of their title of office. From the circumstance of their names being inscribed on the coins, it is reasonable to conclude, that they were responsible for the integrity of the money, and that likewise they were the principal officers of the mint, because inferior officers would have given security to their superiors, whose names would have appeared on the money, as a pledge to the sovereign that it

Coinage. was duly executed. The silence also of the Anglo-Saxon laws, and of Doomsday Book, as to other officers of the mint, whilst they so frequently mention the moneyers, greatly corroborates the opinion, that they were the only persons employed in the Anglo-Saxon and early Anglo-Norman mints, except, perhaps, occasional labourers; and it is observable, that, when in the reign of Henry I. the money was so much corrupted as to call for a sentence of the most exemplary severity on the offenders, the punishment is said to have been inflicted upon moneyers only, without the least notice of any other officer. This was also the case upon a similar occasion in the reign of Henry II.

Mr Rudding is unable to determine the exact period when it became necessary to place some permanent superintending authority in the mint to prevent the bad practices of the moneyers; but it is probable, he says, that such an officer was appointed between the 26th of Henry II., when the moneyers alone were punished for the adulteration of the money, and the 3d of Richard I., when Henry de Cornhill accounted for the profits of the cambium of all England, except Winchester.

It is not improbable that this first warden of the mint was appointed for the purpose of collecting the revenue arising from the seignorage charged upon coinage of bullion.

The object of the warden's appointment might also extend to the inspection of the fabrication of the money, with a view to prevent the master and his moneyers, or the moneyers alone, from taking any undue advantage of the king, or the public, by the adulteration of the coin. The most important officer, however, upon the establishment of the mint, with a view to the maintenance of the standard purity of the coin, is the king's assay master: and there are persons mentioned as holding this office in the 6th of Henry III. As this officer had the assaying of all the bullion after melting for coinage, and after it was coined, it is obvious that the very existence of the credit and honour of the mint and sovereign depended upon the duties he had to perform; and such an officer probably existed from the earliest period of the fabrication of money, though our records do not accurately define the precise date of his appointment.

The next officer of importance in the mint is the comptroller; and the first whom Mr Rudding's researches have discovered, held the office between 5th and 15th of Edward II. His duty, distinct from that of the other officers of the mint, is to make out annually a roll, called usually the comptroll or comptrolment roll, containing an account of all the gold and silver coined, and to deliver it on oath before one of the Barons of the Exchequer. It is always written upon parchment, and forms a permanent record of the coinages of the mint.

The king's clerk and clerk of the papers is the next check officer upon the establishment; as king's clerk, he acts as a check upon the whole process of the coinage, the same as the warden and comptroller; as clerk of the papers, he keeps a book of record of the transactions of the mint. Of the creation of this office we have not been able to find any record.

These are the principal check officers of the mint,

and, no doubt, were appointed as mutual checks upon each other's integrity, and to watch over the interests of the king and other importers of bullion into the mint.

There is another officer upon the establishment, whose duties are important, but of whose origin and appointment we have not been able to find any notice. His title is, the master's assay master, and his duty consists in assaying every ingot of gold and silver brought to the mint for coinage; and upon his integrity the master and worker relies that no bullion shall be received into the office for coinage, but what is conformable to the standard of the realm.

Mr Rudding remarks, Vol. III. p. 1. that, at a very early period of the history of Britain, when the communication between its different parts was extremely imperfect, it became necessary to establish mints and exchanges, not only in the chief city, but also in various other places, for the purpose of supplying the neighbouring districts with money to carry on their commerce. To this necessity alone such establishments are to be ascribed; and accordingly we find that, by degrees, as the communication opened, the subordinate mints and exchanges sunk into disuse, and one fixed in the metropolis was found to be amply sufficient for the supply of the whole kingdom.

Athelstan appears to have been the first monarch who enacted any regulations for the government of the mints. In his laws, which were promulgated about the year 928, he provided that one sort of coin only should be current throughout the kingdom, and granted to various towns, by name, a number of moneyers proportionate to their size and consequence, and to all boroughs of inferior rank one moneyer each.

These mints were under the control of that within the Tower of London, from which, as paramount, the dies were issued; and for which the moneyers paid a regular fee upon every alteration of the coins. They also paid an annual rent, which, in the city of Lincoln, amounted to L.75 (according to the statement of Doomsday Book), a very considerable sum at that time. The rents of the other mints were, however, much inferior to this.

To increase the facility of distributing the coins made at these mints, Exchanges were appointed in various places from whence the new coins were issued, and in which bullion was purchased for the supply of the mint; and it appears that our monarchs claimed the exclusive privilege of purchasing bullion, and appointed proper officers, to whom they delegated that branch of their prerogative.

It appears to have been the duty of these officers, not only to exchange the current coins of one metal for those of another, but also to receive wrought plate and bullion, and foreign coins, according to their fineness respectively; and as the exportation of the coins of the realm was prohibited, they furnished persons going out of the kingdom with foreign coins, in exchange for English, and also supplied merchants and strangers coming into the kingdom with English coins in exchange for foreign. These exchanges of coin were regulated by a table, which was hung up in the exchanger's office.

This office has ceased to exist since the reign of

Charles I. Henry Earl of Holland was the last keeper of the exchanges between England and Ireland.

Besides the officers mentioned, there was another of great importance in early times, who bore the title of Cuneator. Mr Rudding mentions this officer as being hereditary, and, as far as he had discovered, the only one in the mint that was so. The engravers of the dies seem to have been appointed by him, and to have been under his immediate cognizance. By him they were presented to the Barons of Exchequer, before whom they took the usual oath of office; and it was probably his duty to see that all the dies (as well those which were used in the paramount mint, in the Tower of London, as those which were issued from thence to the subordinate mints) were of the same type. This was no doubt a circumstance of great moment, when so many mints were allowed to be worked in various parts of the kingdom. When these mints were abolished, and the mint in the Tower became the only source from whence coins were derived, the office sunk into disuse. By right of office, this officer claimed the old and broken dies as his fee. An officer of a similar kind exists in the mint at this day, who is called clerk of the irons, whose duty it is to superintend the manufacture of the dies for coinage; but he has no power to appoint the engravers of the dies.

In the early history of the mint, as at present, the master of the mint fabricated the coins at certain charges per pound weight. He had his regular establishment of melters and moneyers, to whom he paid certain rates for melting and making the monies, reserving for himself a certain fee for his trouble and responsibility. For, in all his engagements with the Crown, the master had to bear all waste and charges arising in and out of the coinage of gold and silver. Mr Rudding mentions that, in the 10th of Edward III. the workmen of the mint of London petitioned the king for an increase of their allowance for coinage; alleging that, they were at that time at greater expence, and bestowed more labour, in forming the monies, than had been usual in former times, so that they could not maintain and continue such expence and labour, unless their allowance was increased.

The king being willing to grant their petition if just, commanded John de Wyndesore, warden of the mints of London and Canterbury, together with Lapone Roger, and others experienced in such matters, to inquire whether the allowance was sufficient; and if not, to determine what addition should be made; and they were ordered to make their report in Chancery, under their seals, without delay.

A warrant was in consequence issued, and Lapone and Roger Rikeman, exchangers of London, and Stephen Boke, having been examined on oath by the warden, the following report was made: That, having inquired diligently respecting the necessary expences of the master of the mint and the workmen, viz. of alloy, clay, and salt, and other things used in the making of new money, and also of the expences occasioned by the waste arising from the whitening of the halfpennies and farthings, on account of the increase of the alloy, and from the hardening of the metal of the said coins in work-

ing and coining—they were of opinion that the work could not be carried on without an increase of 3d. for each pound at the least; and with that the workmen ought reasonably to be contented. Then, whereas of old they received for all costs, colour, &c. for a pound of halfpennies, 7½d., and for a pound of farthings, 9½d., they would receive for the former 10½d., and for the latter 12½d., so that the master should have of increase 2d., and the workmen 1d.

It was the duty of the warden to take an account of all the bullion of gold and silver entrusted to the master and worker of the mint to be coined; and in this duty he was aided by the comptroller and king's clerk, who in their respective capacities kept books of entries of the receipt of bullion, and its delivery in coin to those who brought the bullion for that purpose. Besides those duties, these check officers had the superintendence of the different processes through which the bullion had to pass, from the assay of the ingot to the delivery of the coin to the importers; and it is more than probable, that in the infancy of the mint, and when the demand for coin was very limited, the whole processes of the coinage were conducted in one apartment; that the master, warden, comptroller, and other principal officers of the mint, accompanied the sovereign from place to place in his dominions, and actually superintended the fabrication of the coin at the mints of the towns where he sojourned. The progressive civilization of the country, the increasing demand for money, and the more permanent residence of the monarchs in London, give the mint of the Tower a predominancy over all others; and these circumstances very probably called for the appointment of other check officers, who are now upon the mint establishment; such as the surveyor of the meltings, whose duties are to superintend the melting of the pots of gold and silver, and to weigh the proportion of fine gold or alloy which may be necessary to produce the standard of the money; to take samples of all pots melted, and take them to the king's assay-master, for him to ascertain if the standard has been adhered to by the melter; and to lock up the said pots, of which samples have been taken, in the melter's strong-hold, of which he has one key, and the melter another, and there to retain them until the king's assay-master has declared that they are of the proper standard. In the infancy of the mint, the duties of this officer were probably performed in the presence of the warden, comptroller, and king's clerk; but the increase of duties in the mint office, in the receipt of bullion and delivering coin, probably rendered it necessary to relieve the principal officers from these duties, as well as from those of another officer, called the surveyor of the moneypresses, whose duties consist in seeing that good dies are used, and clean money made in the coining room.

When these and other officers were in full power, operating as checks upon the coinage, and, consequently, upon the master and worker, they received their salary and fees from the warden, as chief of the check branch of the establishment.

The expenditure for the repairs of buildings, offi-

Coinage. cers' houses, &c. &c. was also paid by the warden of the mint; and his authority for doing so was by the mint indenture, in which these duties are detailed. "And our said Sovereign Lord the King doth will and command, that the warden or wardens of the mint, for the time being, shall content and pay to the officers and ministers aforesaid, such stipends and wages, and such diet, as in schedule limited and appointed, in manner and form, and during such term as in the same expressed; and that thereof he and they shall have due allowance and defalcation upon his or their accounts. And that the said warden or wardens shall make his or their accounts yearly, as well of all and every of his or their receipts, as of his or their payments, and other charges, before the auditors of the mint for the time being, unless it shall please his Majesty otherwise to appoint the same; in which account the same auditors, or others to be appointed by his said Majesty to take the said accounts, shall make unto the said warden or wardens full allowance, defalcation, and discharge, as well for all such sum and sums of money as he or they shall duly prove to have been paid or disbursed for officers' fees and wages, and diet for the said officers, as for any other necessary charges to be employed in and about the making of the said monies, or the repairing of the said offices and houses, necessarily to be employed in the said service, under the avouchment of the said master and comptroller and assay-master, or any two of them, whereof the said master is to be one; and the said accounts so to be made by the said auditors, or by any other of his Majesty's special appointment for the same, being stated, and his debts determined, and his said accounts fully answered to his Majesty, the said warden or wardens, upon his or their suit to the Lord Chancellor, or Lord Keeper of the Great Seal, or Commissioners of the Great Seal, shall have letters patent of his said Majesty under the great seal, to be made on his or their acquittance, without fee therefor paying; for the making of which said letters patent, these presents shall be a sufficient warrant and discharge to the said Lord Chancellor, or Lord Keeper, or Lords Commissioners for the custody of the Great Seal, for the time being, without any further or special warrant to be sued out for the same."

Notwithstanding the number of the checks upon the coinage of our money, its history gives us the most undeniable proofs of their inefficiency, when the arbitrary will of the sovereign was allowed to put all law and justice aside. However much we may admire the precautions used by our ancestors in the formation of the constitution of the mint, we have still the painful recollection (though its forms and regulations have existed since the reign of Edward III.) that they could not prevent a Henry VIII. from disgracing his reign by, perhaps, the most wanton debasement of the currency, that was ever, in a similar period of time, practised in any country in the world. The same ignorance and injustice disgraced the beginning of the reign of his son, Edward VI., but the subsequent acts, even of his short reign, were a good apology for the impolicy of his measures, and the severest censure upon the injustice of his father's acts regarding the currency. The

short reign of Edward VI. prevented that thorough reformation in the currency which the wisdom of his measures began, and which was perfected in the long and glorious reign of his successor, Elizabeth.

Coinage. In the early history of our coinage, its expenses were paid by a duty or seignorage upon the money coined; and, besides these expenses, a certain duty was retained for the sovereign, and was one of the sources of his revenue. The amount of this duty was regulated entirely by the will of the sovereign, and without any regard to the principle by which it was assessed; it varied in different reigns, and was probably, in a great measure, regulated by the necessities of the sovereign for the time being. The mere charge of coinage, as Mr. Rudding justly remarks, is probably as ancient as the invention of coined money; because it would soon be discovered, that the sovereign, after having turned his bullion into coins, for the benefit of his subjects, was no richer than before. It is probable, however, that the deduction did not remain long at the simple expense of coinage, but was soon made a profitable and easily collected source of revenue. In fact, the prerogative of coinage being exclusively the sovereign's, made it a certain source of revenue. In the earliest mint accounts which Mr. Rudding has met with, viz. one of the 6th of Henry III., the profit upon the coinage was 6d. in the pound. This appears, says Mr. Rudding, from the entries, under that year, of bullion coined in the mint at Canterbury, when the profit upon L. 3898, 4d. is stated to be L. 97, 9s., which is exactly 6d. in the pound. Of that sum the king had L. 60, 18s. 3½d., and the archbishop L. 36, 10s. 10½d. (these totals do not precisely agree, as is frequently the case when sums are stated in Roman numerals); the whole sum of L. 97, 9s. is stated to be the amount of exitas lucri, that is, we presume, the clear profit, after all the expenses were deducted. And this will agree with the seignorage which was taken in the 28th year of Edward I., amounting to 1s. 2½d. upon every pound, out of which the master had 5½d. for all expenses, and there remained 9d. clear profit to the king.

As this latter date is about seventy-eight years subsequent to the former, it is not improbable that the seignorage had been raised in that time, in the proportion of nine to six.

A seignorage continued to be charged upon the coinage of both gold and silver until the reign of Charles II., who, after his restoration, took the expenses of the coinage of the money of the Commonwealth upon himself. Regulations introduced by Charles II.

In September 1661, in the 13th year of his reign, a proclamation was issued, declaring, that the gold and silver coined during the period of the Commonwealth should not be current after the last day of November in the same year. At the same time it declared, "that such of our subjects in whose hands these moneys shall be found after the last day of November next ensuing, may not suffer too great damage or prejudice thereby, we are pleased further to declare, that all and every person and persons who shall bring any gold or silver coin of the stamps and inscriptions aforesaid into our mint in the Tower of London, shall there receive

the like quantity of lawful and current moneys, weight for weight, allowing only for the coinage."

On the 7th day of December in the same year, another proclamation was issued, declaring the money of the Commonwealth current only in payment of taxes, &c. to his Majesty, and to continue so to the 1st day of May next ensuing. The object of this proclamation was to bring as much of this money into his Majesty's exchequer as possible, for the purpose of recoining it. It is in this proclamation that the king takes the expence of coinage upon himself: "We being willing," it says, "for the ease of our subjects, to take the charge of the coinage thereof upon ourself."

It was in these proclamations that the system began of charging the government with the expences of the coinage of this country. The merchants and others, who were interested in saving both the duty and the expence of coinage, took advantage of the last mentioned proclamation, and represented to the king and his council by memorials, the great advantage which trade and the country at large would derive from the sovereign taking upon himself, as a permanent charge, the expence of coinage; they also represented that a great increase would take place in the quantity of money, if coined free of any charge to the importers of bullion. As these representations were irreconcilable with the just principles of public wealth,—as they were brought forward by persons ignorant of the consequences which would attend their execution, we much doubt whether they produced the effect which the interested individuals were so desirous of obtaining. In the 18th year of the same reign, an act was passed, exempting, in future, the importers of bullion from all charge of coinage, and which has continued till the present day.

As the science of political economy was very little understood in the period here mentioned, it is not to be wondered at, that the voices of a few interested individuals could procure the passing of an act so plausible. There can be no doubt but Charles and his council were swayed by the apparent knowledge which those individuals evinced in the practical details of business, and trusted to their representations being correct; but a practical knowledge of business, founded upon mistaken principles, must lead to erroneous conclusions; and it is easy to prove, that Charles and his council were imposed upon by these practical men.

This country would, at least, have been equally rich, and the quantity of coined money in no degree diminished, if the charge of workmanship had been continued upon the coinage; for the quantity of money in a country that possesses no mines of its own, must be regulated by the produce of its land and labour,—upon the quantity of exchangeable commodities; and as the quantity of exchangeable commodities increased, so would the quantity of money be increased, except in so far as good husbandry, or increased value of the precious metals could make it be spared to circulate them. As the charge of coinage could have no effect in diminishing the quantity of the precious metals that would be imported into the country; the portion of this bullion that would be brought to the mint to be coined,

would depend upon the demand for coin; and this demand would regulate the profits, which the individuals, who did coin, could make by it, either in trading with it themselves, or by lending it to others.

If there were a charge for coinage, there would, strictly speaking, be a less quantity of bullion imported, because we should have a less quantity of money than we now have; but that money would be more valuable. A guinea or 5 dwts. 9½ grs. would be more valuable than 5 dwts. 9½ grs. of gold bullion, and consequently fewer of them would be requisite for the circulation of the same amount of commodities. The effect would, therefore, be to increase the quantity of commodities, and to lessen the quantity of bullion or coin.

The policy of Charles's measures with respect to the coinage, have been questioned by various writers. And, in fact, the principle of a seignorage, so often agitated, has never been satisfactorily settled. Lord Liverpool, in his excellent Letter to the King upon the Coins of the Realm, conceives that a seignorage upon our gold coin, which is the standard money of our country, would necessarily cause that measure of property to be imperfect. His Lordship has not favoured us with any account of the nature of the imperfection that would have been created by charging a seignorage upon our gold coins. The only imperfection that could be called into existence we apprehend, by charging the expence of coinage upon gold, would be the alteration which it would make in its value. L. 100 of gold coin, chargeable with an expence of coinage (say of 1½ per cent.), would, while the king preserved the monopoly of coinage, be more valuable than its weight of uncoined gold; and consequently would alter the state of debtor and creditor, as well as require the Government to pay her annuitants, and other branches of her expenditure, in a currency more valuable than before the charge of seignorage was imposed.

Let us, for example, suppose that we had only coins of gold in this country, and that a seignorage to the amount of the expences incurred in their manufacture was imposed by the legislature, say of 1½ per cent., it must be evident that a L. 100 of such coins would be more valuable than their weight in bullion of the same purity, by the expence of the coinage. Every L. 100 of such gold currency, therefore, would purchase not only its weight of bullion, but 1½ per cent. more, as the expence of converting such bullion into coin. As no legal coin can be obtained but where this charge is made, the market-price of gold would thus be 1½ per cent. under its mint price. If the seignorage exceeded the expences of the coinage, so as to afford a profit to the illegal coiner, supposing him to coin money of the legal standard in weight and fineness, then would the value of the currency be reduced by such illegal additions to its quantity; the market price of bullion would approach to its mint price, but would fall short of it by the real expences of the coinage, and would thus destroy the profits of the illegal coiner. It will also follow, that a L. 100 of such currency would purchase a greater quantity of any commodity than its weight of bullion of the same purity

Coinage. would do, and that by the expences of the coinage, or $1\backslash frac\{1\}\{2\}$ per cent. By the imposition of a seignorage, therefore, the price of bullion and commodities would experience a fall, limited however by the real expences of the coinage, no laws having yet been devised to prevent illegal additions to the currency. We should not however apprehend that the coins fabricated under this system would in any degree be imperfect: on the contrary, we think that a considerable national advantage might have been the result, had such a principle been adopted at the British mint. As the value of the coins would be increased, so would their quantity have been diminished. A smaller amount of currency would have circulated the same quantity of commodities. The gold thus relieved from the channel of circulation, would, in the hands of individuals, have become capital, the nation deriving all the advantages of its reproduction, with a profit.

The second objection of Lord Liverpool, if well-founded, would certainly render it impolitic in the legislature to enact a seignorage upon the coins constituting the principal measure of property, either as a present or primary principle in the government of the mint. "The merchants of foreign nations, whom may have any commercial intercourse with this country, estimate the value of our coins only according to the intrinsic value of the metal that is in them; so that the British merchant would, in such case, be forced to pay in his exchanges, a compensation for any defect which might be in these coins; and he must necessarily either raise the price of all merchandise and manufactures sold to foreign nations in proportion, or submit to this loss."

If the imposition of a seignorage had no effect in augmenting the value of the coins, Lord Liverpool's objection would be correct; but we have already stated, that the coins acquire a value proportionate to the expence of the coinage; the natural limit of a seignorage where the laws cannot prevent illegal additions to the amount of the currency. If so, the relation between the foreign and British merchant would in no degree be changed; they would continue to buy and sell, with the same advantages as before the seignorage was imposed:—there would, it is true, be some differences in price, but not to affect the relative interests of the parties. For example, if a seignorage of $1\backslash frac\{1\}\{2\}$ per cent. was imposed upon the currency of England, while that of Hamburg remained without alteration, it will be evident, from what has already been stated, that a fall in the price of British commodities would take place in consequence; but this fall in prices would not be confined to British commodities alone; the foreign commodities brought to the English market must necessarily undergo the same reduction; but the foreign merchant would not be subject to any loss in consequence of this fall in the price of his commodities; for the reduction in the price of English goods enables him to buy as much cheaper as will compensate for the diminution in the price of his foreign wares: neither would the British merchant be subject to any loss by the fall in prices, he being enabled to buy foreign commodities so much cheaper as to compensate for the reduction in the price of English commodities.

Coinage. The exchanges with foreign nations would be regulated by the same principle. A merchant in London, for example, wanting to remit L. 100 to his correspondent in Hamburg, to discharge a debt which he owed there, would with his L. 100 of English currency, augmented of $1\backslash frac\{1\}\{2\}$ per cent. in value by a seignorage, buy upon the London Exchange a bill upon Hamburg, entitling him to a quantity of Hamburg currency equal in value to L. 101, 10s.—thus would bills upon Hamburg be said in the London market to be at a discount $1\backslash frac\{1\}\{2\}$ per cent. But England would not gain by this discount upon Hamburg bills; for, let us suppose that a merchant in Hamburg wishes to discharge a debt in London of L. 100, all bills on London, sold in Hamburg, will, upon the same principle, be sold at a premium equal to the increased value of the currency in England, to which these bills entitle the holders of them.

As a nation cannot permanently import to a greater amount than it exports, the holders of bills in London upon Hamburg, cannot permanently exceed the holders of the bills in Hamburg upon London, so that the discount on Hamburg bills in the one case, and the premium on London bills in the other, will necessarily balance each other; so that neither party, if we are correct in our argument, would lose or gain, as far as related to the exchange by the imposition of a seignorage upon the British currency.

The third objection of Lord Liverpool to a seignorage upon the gold currency of England is, "That no such charge of fabrication has taken place at the British mint for nearly a century and a half past; and, if it were now to be taken, the weight of the new gold coins must be diminished to pay for this fabrication."

It does not necessarily follow, that a charge for the fabrication of our gold coins should diminish their weight to pay for such fabrication. If the expence of coining L. 100 of gold currency at the Royal Mint was L. 1, 10s., the individual bringing the bullion to the mint, having this charge to defray, would not sell his L. 100 in coin for its weight in bullion; the value of the coin being augmented by the value of the workmanship, he would readily command a quantity of gold bullion more than its weight by the expence of the coinage, or $1\backslash frac\{1\}\{2\}$ per cent., as has been already stated. This mode would render any change in the weight of the coin unnecessary.

Lord Liverpool's last objection is, "That these new gold coins would either differ in weight from those now in currency, or, to prevent this evil, the whole of our present gold coins must be taken out of circulation, brought to the mint, and be recoined."

If we are correct in our answer to his Lordship's third objection, the last one will necessarily fall to the ground. All the advantages of a seignorage may be obtained, without such seignorage being deducted from the weight of the coins.

From the arguments we have adduced, we should be justified, we apprehend, in approving of the principle of a seignorage, even upon the coins which constitute the principal measure of property, provided it did not exceed the mere expence of the coinage of such coins; for where a seignorage is charged, there is a tendency, as we have already

Coins. noticed, to a fluctuation in the value of that currency,—an evil which should be avoided as much as possible. Where an extensive paper currency is used, as in England, this evil is considerably increased, even though the issuers of it are liable to pay it in specie on the demand of the holders; still both their notes and the coin might be depreciated to the full extent of the seignorage, before the check which limits the circulation of paper could operate. If the seignorage on our gold coin were 5 per cent., for example, the currency, by an abundant issue of bank-notes, might be really depreciated 5 per cent. before it would be the interest of the holders to demand coin for the purpose of melting it into bullion,—the legal check to restore it to its proper value. If the seignorage amounted only to the mere expense of coinage, which is about 10s. per cent., that would be the whole fluctuation in the value of our legal currency, even though bank-notes, payable on demand, formed the most considerable portion of it.

When Charles II. annulled the law for charging a seignorage upon our coins, he must have caused that alteration in the value of property which we here state as the reason why we cannot recur to it again, consistently with our national honour. And the late act respecting coinage, which allows a seignorage to be charged upon silver of 4d. per oz., but which directs that no charge whatever should be made on gold, it being the standard of property, is therefore a wise measure; as it preserves the integrity of that standard which has existed for upwards of a century, and by which the value of all property has been regulated.

If a seignorage, therefore, is ever charged, it should be from the first introduction of coined money in a state, and ought never to fluctuate in amount, as was anciently the case in this country; because such fluctuations must cause as frequent fluctuations in the value of property, an evil which cannot be too carefully avoided.

Improvements in the Machinery during the Reign of Charles II. The next important event in the history of the mint, was the introduction of the mill and screw, which took place soon after the restoration of Charles II. Previous to his reign, the money in circulation was made by forging or hammering slips of gold and silver to the proper degree of thickness, then cutting a square from the slip, which was afterwards rounded and adjusted to the weight of the money to be made; the blank pieces of money were then placed between two dies, containing the design of the coin, and the upper one was struck with a hammer. This money was necessarily imperfect, from the difficulty of placing the two dies exactly over each other when the blank piece was between them, as well as from the improbability of a man being able to strike a blow with such force as to make all parts of the impression equally perfect.

The mill or press was first introduced from France into this country in the reign of Queen Elizabeth, but after a few years use was abandoned, as too expensive, and the hammer coinage resumed.

The coining press or mill is of French origin, and is generally ascribed to Antoine Brucher, an engraver, who in 1553 first tried it in the French King's

(Henry II.) palace at Paris, for the coining of counters. It continued in use till 1585, in the reign of Henry III., when it was laid aside, on account of its being also more expensive than the hammer coinage. The machine remained in disuse until 1623, when Briot, a French artist, who was unable to persuade the French government to adopt it again, came to England, where it was immediately put in practice under Briot's direction, who was appointed chief engraver of the mint.

Like many other new inventions, it was sometimes used, then laid aside, and the hammer resumed for about 40 years. In the year 1662, the mill and screw were completely established in the English mint, as it had been by the French in the year 1645. The great improvement which took place in the form and impression of the coins struck by this new invention, gave them a decided superiority over the hammer money; and the excellent and truly philosophical improvements of the late Mr Boulton, which we shall hereafter describe, have placed the process of coining upon a basis so firm, and so decidedly superior, both in facility and economy, that we have no fear of returning to the ancient and less perfect mode of fabricating our money.

The next important feature in the history of our mint, was the extensive silver recoinage of King William, which amounted to upwards of L.7,000,000 Sterling. It was executed at several country mints, besides the mint in the Tower of London. The principle upon which this recoinage was executed, was a subject of great controversy, and occupied the talents of Mr Locke, Mr Lowndes, and others. Mr Lowndes wished to execute the coinage at a rate per oz. conformable to the market price of silver; overlooking, at the same time, that the market price exceeding its mint price, arose from the deficiency in the weight of those coins by which silver, as well as all other commodities, was bought and sold. Mr Locke, with that acuteness for which he was so justly esteemed, contended that, if 5s. 2d. of the coin weighed an oz. that would necessarily be the market price of silver; and that its high price arose from 6s. 4d. of the then currency containing no more than an oz. of standard silver. Consequently, if the coinage was executed at a rate higher than the standard of the 46th of Elizabeth, or 5s. 2d. per oz. it would be done at the expense of that justice and integrity between the government and the people, which no government would sanction that regarded the rights of personal property. Mr Locke's arguments were so decidedly just, and so convincing, that the government carried the whole nation with them in the measure, though it was heavily felt, owing to the exhausted state of the country, after the long and expensive war it had been involved in.

In the course of a little time after the recoinage was completed, Mr Locke's reasoning was called in question, from the circumstance of the price of silver exceeding its mint price, and the consequent disappearance of the coinage, by melting the coins into ingots for sale at the high market price. As this is an exceedingly curious and interesting portion of the history of our mint affairs, we may be allowed to

Coinage. state a few facts by way of vindicating the accuracy of Mr Locke's theory, and to point out the real cause why its application to practice failed, as it is generally acknowledged that it did; the greater portion of the silver recoinge having, before the year 1717, disappeared from the circulation.

By an Abstract Account of the prices which the Bank of England paid for gold and silver bullion in each year, from 1697 to 1811, it appears, that, as early as 1710, they paid L. 4 per oz. for standard gold, and 5s. 3d. for standard silver; and, it is probable, that the same price existed at a more early date after the recoinge, though the accounts state no price before 1710. This account we conceive of very great importance, and, we think, will satisfactorily explain why Mr Locke's theory did not permanently produce the effect which the legislature expected from it.

By a reference to the prices paid for gold by the Bank of England from 1710 to 1717, it appears, that the average price per oz. was L. 3, 19s. 11d. During this period, the guinea was current for 21s. 6d., at which rate the oz. of gold was coined into L. 3, 19s. 8$\backslash frac\{1\}\{2\}$d.; for, if one guinea or 5 dwts. 9$\backslash frac\{1\}\{2\}$ grs. be worth 21s. 6d., 480 grs. or 1 oz. will be worth L. 3, 19s. 8$\backslash frac\{1\}\{2\}$d. It would appear, then, that the market price of gold was only 2$\backslash frac\{1\}\{2\}$d. above its mint price; and some debasement by wear may have existed upon the gold currency at this period, causing such excess of the mint price.

While the mint, therefore, coined gold at the rate of L. 3, 19s. 8$\backslash frac\{1\}\{2\}$d. per oz., and silver at 5s. 2d., the relative proportion was as 15.43 to 1. There is only one quotation of silver given for the period in question, and it is 5s. 3d. per oz. If we take this as the average price for the seven years in question (and we may be justified in doing so by the market prices which follow in 1718 and subsequent years, as extracted from Castaign's Papers, and laid before the House of Commons, and ordered to be printed 4th March 1811), at 5s. 3d. per oz., the average proportion of gold and silver in the market would be 15.22 to 1. But no individual would carry 15.22 ozs. of silver to the mint to be coined into about L. 3, 18s. 7d. when these 15.22 of silver would procure an ounce of standard gold in the market, which could be coined into L. 3, 19s. 8$\backslash frac\{1\}\{2\}$d. making thereby a profit of about L. 1, 7s. 6d. per cent. While this profit continued, it may reasonably be inferred that gold, and not silver, would be the standard of our money.

It was in September 1717, that Sir Isaac Newton delivered in his Report to the Lords of the Treasury, giving it as his opinion, that gold was considerably overrated in the mint with respect to silver; and, in consequence of this report, the guinea was, by proclamation, dated 22d December 1717, declared current at 21s. It is of importance to observe the effect produced upon the price of gold by this proclamation; and we are of opinion it will completely prove, that the silver currency had not operated as the standard of value during the period in question. When the guinea became a legal tender at 21s., the price of gold became fixed at L. 3, 17s. 10$\backslash frac\{1\}\{2\}$d. per oz. at the mint; for, if 5 dwts. 9$\backslash frac\{1\}\{2\}$ grs. be worth 21s., 480 grs. or 1 oz. will be worth L. 3, 17s. 10$\backslash frac\{1\}\{2\}$d. This

fall in the price of gold from L. 3, 19s. 8$\backslash frac\{1\}\{2\}$d. is 1s. 10$\backslash frac\{1\}\{2\}$d. per oz., and is equal to about L. 2, 6s. per cent. It appears by the abstract of prices paid for bullion by the Bank of England, that in 1718 and subsequent years they paid L. 3, 18s. per oz. for standard gold, which is a fall from L. 3, 19s. 8$\backslash frac\{1\}\{2\}$d. of 1s. 8$\backslash frac\{1\}\{2\}$d. per oz.; and if an allowance is made for the debasement by wear, existing at this period upon the gold coin, the fall in the market price of gold will be equal to the reduction in the value of the guinea. But this effect could not have been produced unless gold at the period in question had been the measure of value, and, as such, the measure of its own price.

From these facts, we think the conclusion may be justified, that from 1710, and probably a more early period after the recoinge, to the date of Sir I. Newton's report, the gold money of this country was the standard measure of property; and that the reduction of the value of the guinea, thereby making the relative proportion of gold and silver approximate nearer to those of the market, was the first step of which we have an authentic record, taken by Government to maintain the principles of Mr Locke's theory: and as the avowed intention of this report was to give that rise in value to the silver coin which would protect it from the melting pot, and which could be done by lowering that of gold, it may be inferred, that the legislature were aware that the gold coin had attained the prerogative of being the standard of value at this time. Though the recommendation in Sir I. Newton's report was carried into effect, by making the guinea current at 21s., yet it did not restore silver to its function as the standard of our money; and this, because the current value was not made still lower. Sir I. Newton seemed aware of this himself, and recommended that 10d. or 12d. should be taken from the guinea instead of 6d. This however was not done; and, as the rate of 21s. to the guinea, the proportion of standard gold to standard silver, at the mint, was as 15.07 to 1, the proportion of the market, as we find by the prices of gold and silver at this period in Castaign's Papers, was about 14$\backslash frac\{1\}\{2\}$d. to 1; which constitutes a difference of about 3 per cent., gold being still thus much rated above its value to silver; and consequently, not only was no silver coined, but the good and heavy coins were still melted for the high price they brought in the state of bullion. It is surprising that the Government, having seen the operation of the principle recommended in the report of Sir I. Newton, did not carry it a little further, and bring the current value of the guinea to a par with the market proportion of the two metals, and so render it the interest of the public to carry silver to the mint to be coined.

Before concluding our observations upon this highly interesting subject, we must remark, that the great Mr Locke himself did not impute the high price of silver, after the recoinge, to the cause to which we have here assigned it. He attributed it to the permission of exporting silver bullion, and to the prohibition of exporting silver coin. This permission, he said, rendered the demand for silver bullion greater than the demand for silver coin. Dr Adam Smith remarks upon this opinion, that the number of

people who want silver coin for the common uses of buying and selling at home, is surely much greater than that of those who want silver bullion, either for the use of exportation, or any other use. There subsists at present a like permission of exporting gold bullion, and a like prohibition of exporting gold coin; and yet the price of gold bullion has fallen below the mint price. But in the English coin, silver was then, in the same manner as now, underrated in proportion to gold; and the gold coin (which at that time was not supposed to require any reformation) regulated then, as well as now, the real value of the whole coin.

No other legislative measure having been taken than what we have mentioned, founded upon the Report of Sir I. Newton, and the market proportion of gold to silver having seldom rendered it the interest of the public to coin silver; this accounts satisfactorily for the degraded state of our silver currency for the last century.

In the year 1774 and subsequent years, we had a general recoinage of our gold currency, which forms the next prominent feature of our mint history. The avowed object of this recoinage was a reformation of the light and defective coins then in circulation; and the motive for doing so was to prevent the new and heavy coins from being selected from the circulation, and melted for the high price which the gold brought in the state of bullion. In fact, L. 4 of the gold coin then in circulation would not weigh more than an ounce; and, by reference to the prices paid by the bank for gold, we find that this was the market price. The holders of bank notes demanding new and heavy coins for them, required the bank to have a large coinage of gold annually, to supply this demand. These coins were melted, and sold in the state of bullion to the bank for the high price of L. 4 per oz. To remedy this inconvenience, the recoinage was completed. And it had the effect desired; for the price of gold, for upwards of twenty years, never exceeded, but was rather under its mint price.

Political economists have disagreed as to the cause of the high price of gold previous to the recoinage. Dr Smith says, "By issuing too great a quantity of paper, of which the excess was continually returning, in order to be exchanged for gold and silver, the Bank of England was for many years together obliged to coin gold to the extent of between eight hundred thousand and a million a year; or, at an average, about eight hundred and fifty thousand pounds. For this great coinage the bank, in consequence of the worn and degraded state into which the gold coin had fallen a few years ago, was obliged frequently to purchase bullion at the high price of L. 4 per oz., which it soon after issued in coin at L. 3, 17s. 10$\backslash frac\{1\}\{2\}$d. an oz.; losing in this manner between 2$\backslash frac\{1\}\{2\}$ and 3 per cent. upon the coinage of so very large a sum. Though the bank, therefore, paid no seigniorage, though the Government was properly at the expence of the coinage, this liberality of Government did not prevent altogether the expence of the bank."

Mr Ricardo very justly remarks upon this passage, that, "on the principle above stated, it ap-

pears most clear, that, by not reissuing the paper thus brought in, the value of the whole currency, of the degraded as well as the new gold coin, would have been raised; when all demands on the bank would have ceased; or, in other words, the price of gold would have fallen to its mint price.

Mr Buchanan is not of this opinion; for he says, "that the great expence to which the bank was at this time exposed was occasioned, not, as Dr Smith seems to imagine, by any imprudent issue of paper, but by the debased state of the currency, and the consequent high price of bullion. The bank, it will be observed, having no other way of procuring guineas but by sending bullion to the mint to be coined, was always forced to issue new coined guineas in exchange for its returned notes; and when the currency was generally deficient in weight, and the price of bullion high in proportion, it became profitable to draw these heavy guineas from the bank in exchange for its paper; to convert them into bullion, and to sell them with a profit for bank paper, to be again returned to the bank for a new supply of guineas, which were again melted and sold. To this drain of specie the bank must always be exposed while the currency is deficient in weight, as both an easy and a certain profit then arises from the constant interchange of paper for specie. It may be remarked, however, that to whatever inconvenience and expence the bank was then exposed by the drain of its specie, it never was imagined necessary to rescind the obligation to pay money for notes."

Mr Ricardo remarks upon this passage, that "Mr Buchanan evidently thinks that the whole currency must necessarily be brought down to the level of the value of the debased pieces; but surely by a diminution of the quantity of the currency, the whole that remains can be elevated to the value of the best pieces." With this opinion of Mr Ricardo we cordially agree, and it is upon this principle that a seigniorage can be laid upon coinage, without any one directly paying for it as a tax. By restricting the quantity of a currency, this seigniorage may be 10, 20, or even 50 per cent., and the price of gold neither raised above its mint price, nor the bank subjected to a run for guineas.

During the period of these important transactions, the constitution of the mint remained without alteration. It had not, however, escaped the attention of the legislature, for we find that, on the 7th February 1798, his Majesty, by an order in Council, was pleased to appoint a Committee of his Privy-Council "to take into consideration the state of the coins of this kingdom, and the present establishment and constitution of his Majesty's mint." The first effort of this committee was to advise the erection of a new mint, with improved machinery, which desirable object was accomplished between the years 1805 and 1810: And in March 1815, a new constitution was introduced, founded upon a very valuable Report, drawn up and presented to this Committee by the Right Honourable W. Wellesley Pole, who had been appointed Master of the Mint in the preceding year.

We cannot better explain the whole constitution

Coinage and bearings of the establishment, than by detailing the rules, regulations, and instructions, applicable to the duties of the different departments.

The proper duties of the Deputy-Master and Worker are,

To receive, on account of the master and worker, his Majesty's own bullion of gold and silver, as well as the bullion of any other person, brought to the mint for coinage:

To give acknowledgments for the same, specifying the number of ingots, or parcels of coin, according to the purport of any invoice or bill delivered therewith:

To see the ingots safely deposited in the care and joint custody of himself and the master's assayer, for the purpose of being assayed previous to their importation into the office of receipt:

To cause the ingots, when duly assayed, to be brought into the office of receipt without delay, there to be weighed in the presence of the importers and cheque officers:

To make out a mint bill, to be delivered to the importer, testifying the weight, fineness, and value of the several ingots, &c. together with the day and order of the delivery into the mint, and to sign a receipt annexed to the said bill, witnessed by the Comptroller and King's clerk:

To give directions to the master's first clerk, for the combining or potting the ingots for the melting, with the proper portion of alloy; and to see that the same be duly entered by the said first clerk and melter, in the pot-book, and the said book examined by the Comptroller and King's clerk; and to deliver out of the strong-hold such ingots and bullion as are potted, and charge the melter therewith, according to the standard weight of each pot:

To keep an account of the bars received from the melting-house, and delivered to the moneyers, and also of the scissell returned by the moneyers to the melter, for which their respective receipts will be given and entered in the pot-book, that they may be charged therewith:

To receive the coined monies from the moneyers, after the same have been duly tried at the pix by the King's assayer, Comptroller and King's clerk; and to deliver the same to the importer, receiving back at the same time the mint bill which had been given; or if the same be not cleared off, to require that such portion thereof as has been delivered, be indorsed on the bill by the parties, by a receipt, till the whole be discharged:

To seal and lock up in the usual chest, in conjunction with the King's assayer and comptroller, the pieces reserved for the public trial of the pix, and to make good to the parties the pieces so taken, by payment in their sterling value; charging the same to the public expence:

As first executive officer of the mint, to watch over every branch of the department, and to inspect and oversee, as much as lies in his power, the meltings, assayings, and all the different processes of the coinage, and to report to the master on the conduct of the officers:

To draw and indite all letters, instructions, com-

missions, and other writings agreed upon and ordered by the master and worker, for the service of the office, and to have the same recorded by the clerk of the papers:

To receive all monies issued at the exchequer or elsewhere, for the service of the mint; and to keep the public account of the master, to be laid annually before the auditors of public accounts, with the proper vouchers, the said account to be signed and attested by the master himself:

To make quarter books of the salaries, wages, allowances, &c. due to the several officers, clerks, artificers, and others belonging to the establishment; and to make payment thereof on the quarter days, namely the 5th of January, the 5th of April, the 5th of July, and 10th of October, whenever there shall be funds for that purpose: Also, to pay the moneyers and melters charges for coinage, according to the rates set forth in their respective agreements with the master; the same to be payable out of the monies issued for the service of the mint, the salaries, &c. being previously discharged: Also, to pay the incidental expences and disbursements usually incurred in the different offices; and to pay the solicitor his account for disbursements in carrying on prosecutions for offences against the laws relating to the coin, out of such monies as shall be impressed from time to time, for that service, exclusive of the ordinary allowance:

To receive all the fees arising to the master's office under the indenture or otherwise, and to apply the said fees to the payment of the master's salary, in the manner directed by the act 39th Geo. III. and to account for the same to the Lords Commissioners of his Majesty's Treasury, by half-yearly statements, showing the deficiency of the fees, and the sum to be provided, or the excess, as may happen; and to make out a yearly account to the Treasury:

For this office he is to give the usual security, or such other as may be required by the Lords of the Treasury:

In conjunction with the comptroller, to inspect and examine the accounts of the clerk of the irons, as to the dies supplied to the engraver and moneyers, and the faulty ones destroyed:

To attend the duties prescribed by the act 14th Geo. III. respecting the standard money weights.

The proper duties of the King's Assayer are,

To keep a book of the assays made by him, of all such gold and silver as may be brought into the mint, whereby the quantity and fineness may appear:

If the master of the mint, or the merchant, or importer, who brings his gold or silver for coinage, may not accord between them of the true value of the bullion, or if it be not malleable and fit for working, or sufficiently nigh to the standard, according to the customs of the mint, the King's assayer is to try the truth in that part, in the presence of the master and comptroller, and the master shall receive the same in manner as it becomes:

To report (after the bullion has been weighed, potted, and melted) the assay of every several pot, commonly called the pot assay, which pot assay

shall be made of some bar of the said bullion, to be taken by the comptroller, the King's assayer, or surveyor of meltings, or any one of them, after the pot is cast out; the said report to be made in writing, and delivered through the office to the surveyor of meltings:

To take care that the bars of gold and silver be melted, and the monies made agreeably in fineness, to the indented trial plates, made by direction, and ordered to be used by the royal authority; whereof one trial plate for the gold, and one for the silver, shall remain with the King's assayer:

In conjunction with the other principal officers to oversee and survey the assaying, and melting, and making the monies, at all times and in all places; and endeavour and procure that the said monies, and every of them, shall be properly made and perfected:

To see and procure, with the comptroller, and weigher, and teller, that the balances and weights be put to point from time to time, when they shall need it; so that no default be found in them, to the hurt of his Majesty and his people:

To make proof (by a process called the pixing) of the monies before their deliverance to the bringers in of the bullion; the said proof to be made in the presence of the master and worker, comptroller, and King's clerk, by an assay to be taken of the fineness as well as of the weight, by such quantity, and after such sort as shall be agreed on, or as has been customary, namely, by weighing the pound weight in tale; and taking one piece out of every journey weight of gold and silver respectively for the assay of the fineness, as directed by the mint regulations. To report thereon, and the report to be entered in the pix books:

In conjunction with the master, and worker, and comptroller, to see a portion, namely, one piece out of every journey weight of the said monies (after they have been proved to be good), ensealed in a packet, and put into a box (called the pix-box), to be locked up under the separate keys of the said officers, there to remain until trial thereof by jury (called the trial of the pix) shall be made before the King, or such of his council as are usually appointed at Westminster, or elsewhere, for that purpose:

He shall be bound to instruct in the art of assaying, the probationer assayer, who shall be nominated by the King's assayer, and approved by the master and worker:

To attend the duties prescribed by act 14th Geo. III. respecting the standard money weights.

The proper duties of the Comptroller are,

To enter on record in a journal or ledger, all such bullion of gold and silver as shall, from time to time, be brought into the mint, which entry shall comprehend the weight as declared by the weigher and teller; the fineness as reported by the master's assayer; and the value of the said bullion, the parties names that brought it, and what day:

To deposit at the office of receipt in the strong-hold, of which he shall possess a key (in conjunction with the deputy-master and worker, and King's clerk), the bullion, after it shall have been received,

and the assays and weight thereof made, reported, and entered, there to remain until it is required to be delivered by the deputy-master for the meltings:

In conjunction with the King's clerk, to take an account of the ingots delivered by the deputy-master out of the strong-hold for the meltings, according to the entry made by the master's first clerk and melter in the pot-book, and to examine the said book as to the calculations of the quantities and fineness, of all manner of gold and silver and alloy, combined and put to each pot respectively for the meltings, and to subscribe the same with his initials:

To take also an account and oversee the weighings of the bars and scissell, passed through the office between the melter and moneyers; for which their respective receipts shall be entered in the pot-book:

To keep an account of all the deliveries of the monies, and to ascertain, at the end of every month or oftener, the balances due by the master to the several importers, and also the balances in the hands of the moneyers and melter, and agree the same with the deputy-master, who is to charge the said moneyers and melter therewith accordingly:

In conjunction with the other principal officers, to oversee the melting, rolling, sizing, and making, the monies, at all times and in all places; and endeavour and procure that the said monies and every of them shall be properly made and perfected:

To see and procure, with the King's assayer, and weigher, and teller, that the balances and weights shall be put to point from time to time when they shall need it, so that no default be found to the hurt of his Majesty or his people:

To attend the proof and trial (called pixing) of the monies before their deliverance to the importer, and to try the weight of some of the pieces in each journey weight singly, as a check that there may be no great variation from the true weight; and also to retain two pieces from each journey weight, one to be delivered to the King's assayer for his assay, and the other to be locked in the pix-box, to be tried before the King or his council—to document the parcel containing the pieces for the pix, and with the other officers enseal the same, and lock it in the pix-box:

To deliver upon oath, before one of the Barons of Exchequer, a roll, which shall be called a Comptroller's Roll, containing an account of all the gold and silver monies coined monthly in the said mint:

In conjunction with the deputy-master to inspect and examine the accounts of the clerk of the irons, as to the dies supplied to the engraver and moneyers, and that the faulty ones be destroyed:

To attend the duties prescribed by act 14th Geo. III. respecting the standard money-weights.

The proper duties of the Superintendent of Machinery and Clerk of the Irons are,

To inspect, from time to time, the several steam-engines and boilers, and the machinery, apparatus, and implements, used in the coinage, and to see that the same are kept in proper order for immediate working, at all times:

To oversee and direct, in conjunction with the

Coinage. company of moneyers, the artificers and workmen employed by Government about the machinery, in doing all manner of work that may be expedient; and likewise in the construction of all the smaller implements and tools necessary to carry on the coinage, upon the principle of the machinery erected; the repairs and work being ordered under the authority of the master and board of mint officers:

To superintend the working of the machinery, and instruct (to the best of his ability) the officers and moneyers in the use and management of it; and to report to the board upon any neglect or misuse:

To examine the several accounts of expences incurred in the machinery,—certifying, in pursuance of the agreements entered into between the master and the moneyers, the charges, both in respect to the bills, and also the wages to the artificers, which shall respectively be borne both by the Government and the moneyers.

As Clerk of the Irons,

To superintend the die press-rooms, and purchase, or procure to be forged, at the cheapest rate, to be approved by the board, all such dies as shall be ordered by the board, and to take care that the same are of the best quality, and properly forged:

To oversee the workmen in the die press-room, and that the dies be skilfully sunk and hardened, and properly turned; and to attend to all matters and things for the well ordering and conducting this service:

To keep a true account of all the blank dies, matrices, and puncheons, for coinage, which shall be delivered to the engravers, or that shall be sunk or stamped by the engravers, and after stamping made fit for use and hardened:

To require the engravers, monthly, to return as many dies as shall be found faulty and worn:

To give an account, as often as required, to the master and comptroller, of the blank dies delivered to the engravers, and the faulty ones returned, that a just account may be kept, and all the faulty dies defaced:

To unlock, and be present, whenever the great die-press for multiplying the dies is used; to be responsible for its not being applied for improper purposes; and that no medals, pattern-pieces, or coin of any description be struck, but by a written order from the master or his deputy.

The proper duties of the King's Clerk, and Clerk of the Papers, are,

To attend the weighings in, and enter in his ledger-book an account of all such bullion of gold and silver, as shall be brought into the mint, describing the weight and fineness as reported, the parties names that brought it, and the day:

To deposit at the office of receipt in the stronghold, of which he shall possess a key in conjunction with the deputy-master and comptroller, the bullion, after it shall have been weighed in, and the weight and assays reported; there to remain until it shall be required to be delivered over by the deputy-master for the meltings:

Coinage. In conjunction with the comptroller, to take an account of the ingots delivered by the deputy-master to the melter, as set down in the pot-book, and to examine the calculations of the pot-book as to the quantities and fineness of all manner of gold, and silver, and alloy, put to each pot, and to subscribe the same with his initials:

Also to take an account and oversee the weighing of the bars and scissell passed through the office between the melter and moneyers, for which their respective receipts shall be entered in the pot-book:

To attend the pix and deliverance of the monies, and record the same, and agree the master's, melter's, and moneyer's balances, up to the end of every month:

To enter (as clerk of the papers) in the record-book, all office-letters, papers, appointments, warrants, and proceedings of the board:

To assist the deputy-master in the secretary department, and instruct the master's second clerk in the keeping the proper entries of bills and accounts for expences incurred, or in making copies of all such papers as shall be required by the master or his deputy, or by the board.

General Instructions for the common duties of the Principal Officers (before-mentioned), to be by them observed.

To make their ordinary habitations and abode in the houses assigned them within the mint:

To meet in the board-room at the mint office every Wednesday (after the delivery of the monies), or on such other day and hour as the master, or the service of the mint, shall require, there to form a board. Three members (the master or his deputy being one) are competent to act:

To consult together, and order all business appertaining to them concerning the office, determining the hours of attendance of the several officers, the receipts of the bullion, and the delivery of coin:

To consider and give directions to the solicitor of the mint, from information laid by him before the board, for undertaking prosecutions for offences relating to the coin, and require him to report, from time to time, as to the state of the prosecutions and convictions:

To take up and employ such smiths, workmen, and labourers as may be severally wanted in the die department and assay offices; and for assisting in the portage and weighing of the bullion and coin in the office of receipt, and to order the superintendent of machinery and clerk of the iron, to purchase or procure to be forged, all such dies as are necessary for the coinage or service of the mint, and to provide all necessaries, and do all manner of business within the mint, as may be needful:

To observe, follow, and perform, all orders, warrants, or significations of the master and worker, whether grounded upon warrants from the King, the Lords of the Committee of Council for coin, or the Lords Commissioners of the Treasury; and in all things to obey jointly or severally, in their respective places, such directions as he shall from time to time judge necessary and fit to give for the service of the mint:

To see that the accounts of the office for the receipt of the bullion and delivery of the coin, as well as the check and control thereof, be kept in due manner, as prescribed, and that the comptrolment roll of the monies, coined monthly, be exhibited yearly to the auditors of public accounts:

To see also that the receipts and payments of all monies for the service of the mint, be charged and accounted for in the master's public account, and that all bills, accounts, and statements, belonging thereto, be examined and allowed under at least three signatures of the principal officers, of which the master's deputy is to be one, previously to its being laid before the audit office:

Also to examine and report to the Lords Commissioners of the Treasury on the fees derived to the master's office; and the application thereof, pursuant to the act 39th Geo. III. as stated in the receiver's account; in order that the same may be declared and passed:

To prescribe to the under officers and servants, their several charges and duties, and to see the due performance of them, and in case of negligence or unfaithful conduct, to report to the master; or, as far as the board are authorized, remove them from their situations:

Not to suffer the works of the mint to be viewed without an order signed by the master; or any stranger or foreigner, not having business at the mint, without knowledge of his quality, to have intercourse with the officers while performing their duties.

The proper duties of the Master's Assayer are,

To receive from the master and worker all manner of gold and silver ingots brought to the mint:

To deposit the same in the joint custody of the deputy-master and himself, in the strong-hold of the assay office, till the assays are made:

To cut one or more pieces from each ingot (as he may think proper), and assay the same:

To make written reports of the assay of each ingot, describing the fineness, date, and name or mark of the importer, and keep a record thereof. To make also such remarks on the quality of the bullion as may be needful for the master's information, and to deliver the list usually given by the importer, of the purchase assays:

To give instructions for the classing of certain of the ingots together, so that the bullion may be mixed and worked as close to the standard as possible, and advantages procured by the mint assay:

To deliver the ingot when assayed into the office of receipt:

The proper duties of the Master's First Clerk and Melter are,

To superintend and carry on the operations of the meltings and refinings, according to agreements (stating the prices and conditions) to be made from time to time between the master and melter:

To attend the weighings in at the office, and rate and standard the ingots in conjunction with the other officers; and their several accounts agreeing, to enter the same in his journal; so that no difference may

arise between the deputy-master and himself as to the value of the bullion to be delivered to melt:

To arrange under the direction of the deputy-master from the said journal, and from the list of ingots classed by the master's assayer, the combination of the bullion for melting, and to make the proper calculations of the quantities and fineness of all manner of gold and silver and alloy put to each respective pot, and to enter the same fairly in a book (called the pot-book), and subscribe his initials to each pot so made up:

To receive the bullion so prepared from the deputy-master, to be deposited and melted under the joint custody and inspection of himself and the surveyor of meltings:

To melt and cast the bars (according to agreement), and, after they have been assayed and reported standard by the King's assayer, to deliver them into the office of receipt; there to be weighed by the weigher and teller, in presence of a cheque officer, and passed to the moneyers:

To receive the returns of scissell, light work, and ends (according to agreement), from the moneyers, to be weighed in like manner, the receipts between the moneyers and melter for the bar and scissell being entered in the pot-book:

To receive from the deputy-master all such gold and silver as may be necessary to refine; to make up an account in the pot-book of each charge, showing the standard amount, to be signed with his initials, and examined by the comptroller and King's clerk; and to supply a quantity of fine ingots, equal in standard weight by computation to the amount delivered to refine, the same to be assayed by the master's assayer, and weighed into the office of receipt, and rated and standardised so as to combine and pot with the coarse ingots:

To agree the balances remaining in his hands with the deputy-master, at the end of each month:

To employ and instruct the master's second clerk in the art of melting bullion; and lastly, to be ready to do his work at all times, when he shall be warned by the master and worker; and to attend to his Majesty's service as need shall require, both morning and afternoon, and to work so many hours every day (Sunday excepted) at such tasks as shall be thought fit by the master, and appointed by the board.

The proper duties of the Provost and Company of Moneyers are,

To superintend and carry on jointly as a company the several processes for the manufacture of the coin, in the rolling, annealing, blanching, cutting out, sizing, and stamping, according to agreements (specifying the prices and conditions) to be made, from time to time, between the master and worker, and the provost and company:

To receive the standard bars of gold and silver for making the monies, from the melter at the office of receipt, there to be weighed by the weigher and teller, in the presence of a cheque officer, and to give receipts for the same, to be entered in the pot-book:

To coin such quantities of the different species of the monies as shall be directed by the master (ac-

Coinage. cording to agreement), and to bring the said monies (in clean pieces) into the office of receipt, in journey weights; there to be tried at the pix and weighed:

To deliver the monies proportionally in weight, according to the bars received; and if any thing lack of the weight at the time of deliverance, to content and pay unto the master the balance at the time of the delivery:

To make out of the bars which shall be delivered to them clean and fit to be wrought, seven twelfth parts into money, so that there be but five parts in twelve scissell:

To return the scissell, light work, and ends to be remelted, proportionally (according to agreement); the same to be delivered into the office of receipt, to be weighed by the weigher and teller, in the presence of a check officer, and to take receipts from the melter, to be entered in the pot-book:

To agree with the deputy-master, the balance remaining in their hands at the end of each month, that they may be charged therewith; and from time to time (as the master shall require) make full payment and deliverance of all manner of monies, with all convenient speed, in order to discharge the said balances, or bring in sufficient supplies of gold and silver, bullion, or ingots, equal in value, according to the weight and assay to be made thereof at the time:

Not to take either singly by the provost, or jointly by the company, any apprentice to be instructed in the art or mystery of a moneyer, or any part thereof, without the licence and permission of the master first had and obtained under his hand in writing:

To oversee, in conjunction with the superintendent of machinery, who is to direct the same, the artificers employed by government about the machinery, in doing all manner of work that may be expedient, and in the construction of the smaller tools and implements for the coinage:

To be ready to do their work at all times without denial, when they shall be warned by the master:

Duly to attend his Majesty's service, in the present way of coining, as need shall require, both morning and afternoon; and to work at such tasks, and so many hours every day (Sunday only excepted), as shall be thought fit by the master, and appointed by the board, according to the labour of their respective tasks, and the length of days:

Neither the provost, nor any of the moneyers, their apprentices or servants, at any time, to vend, pay, or distribute any piece or pieces of the coined monies, until the same shall have been delivered by them, according to the course of the mint, into the office of receipt, and duly assayed and pixed.

The proper duties of the Chief Engraver are,

To make and frame such draughts and embossments, or receive such models for engraving, as the master shall direct:

To engrave from the said designs or models all such matrixes and dies as the master shall direct, and the service of the mint require:

To oversee from time to time the multiplication of the puncheons and dies, in the die press-room, and to receive the dies from the superintendent

and clerk of the irons, that they may be delivered to the surveyor of the money presses in a proper state for the use of the coinage:

To return monthly to the superintendent and clerk of the irons, as many dies as shall from time to time be found faulty, and worn by using or otherwise:

Not to work, or make, or grave any puncheons, matrixes, dies, or stamps, for the making or coining of any money, but only in such places in the mint as shall have been assigned thereunto:

To oversee the striking of the monies in the coining press-room, and to direct all such dies as are faulty to be taken out of the press, and fresh dies put in, that the monies may be properly struck.

The proper duties of the Weigher and Teller are,

To weigh at the office of receipt, under the master's direction, all manner of bullion brought to the mint to be coined, or for the service of the King:

To weigh the bullion, according to such weight or draught (near to a journey weight) as has been customary:

All importations to be weighed in the presence of the deputy-master, or master's clerk, comptroller, or King's clerk, and the importer, who is to state the weight of each ingot from his list, for the guidance of the weigher:

To declare the weight aloud from his scale, that the same may be taken down by the officers and importers:

In conjunction with the other officers, to see that the bullion is free from dirt, and in a fit state for weighing, and to do strict justice, as much as in him lies, between the parties:

To weigh the bars and scissell, passed between the moneyers and melters, and declare the weight of each draught; and also all supplies of fine ingots received from the melter; and the balance or supplies of ingots, &c. made from time to time by the moneyers and melter:

To weigh the coined monies from the moneyers to be delivered to the importers in even journey weights, or to declare the plus or minus on each draught, that the same may be recorded, and the moneyers made answerable for the deficiency of weight or balance at the time of deliverance:

To attend the pix, and tell out the number of pieces contained in a pound weight Troy of the respective species of monies to be delivered to the King's assayer for trial:

To undertake by himself, or by a proper workman in the mint (according to an agreement of prices and conditions), to clean and adjust the beams, &c. in the office of receipt, and to keep the same in order, so that they be always ready and perfect for working.

The proper duties of the Surveyor of Meltings are,

To survey the meltings of all gold and silver, and to take care that the ingots or bullion, according to the number and description in the pot-book, with their proper alloy only, to be weighed by himself, be put into the pot they are respectively set out for:

To see that nothing but scissell or such returns of ends as be clean and good, of gold and silver, respectively, be put into the pots of scissell:

During the time the pots are melting not to absent himself, or to be out of view of the pots so melting, until they have been poured off:

To take two or more assay pieces from some bar or portion of each pot cast from the top, middle, or bottom, of the pot, as agreed with the King's assayer:

To fold up each assay-piece in a paper, docqueted with a description of the ingots and alloy, or scissell, &c. melted in each pot, the number of the pot and the date, and to deliver the same to the King's assayer:

To possess a key of the strong-holds in the melting house, and not to suffer any bars of gold or silver to be delivered out of his custody, until such time as they have been duly assayed and reported good, which reports will be made to him in written notices, transmitted through the office by the King's assayer:

To keep a book containing the weight of all gold and silver as shall be molten from time to time, with the alloys put into the same.

The proper duties of the Surveyor of the Money Presses are,

To inspect the coining presses, and to have a distinct and separate lock upon each of the presses:

To be present at the striking of the monies, and not to suffer the presses to be used for striking any pieces or coins but such as the master shall direct:

To have the custody of the dies received from the engraver and clerk of the irons, to give out the same for coinage, and return the faulty ones to the chief engraver, to be delivered to the clerk of the irons:

To polish the dies, or oversee the doing of the same, when the moneyers are coining:

To inspect the monies, that they be well made and free from brokages, and faulty or dirty pieces; and to do, execute, and perform, all such other works and services in the said office as the master shall direct and appoint.

The duties of the Probationer Assayer are,

To receive instructions from the King's assayer for acquiring a knowledge and proficiency in the art of assaying:

To do all such services in carrying on the business of the assay-office, as the King's assayer shall require, and the master direct.

The duties of the Master's Second Clerk are,

To make out fair copies and entries of all such accounts and papers as might be required in the master's office, and to do all such services in the said office, as the master or deputy-master shall direct or appoint:

To receive instructions from the master's first clerk and melter in the art and undertaking of the meltings.

The duties of the Assistant Engraver are,

To assist the chief engraver in the engraving of the

reverses, lettering, or such other parts of the dies as the chief engraver shall appoint:

To receive instruction from the chief engraver in the art of engraving, and to render all such services in the department as the chief engraver shall require, and the master direct.

The duties of the Mint or Bullion-Porter are,

To attend the office daily, if required:

To be present at all importations and deliveries at the office:

To mark on the assay paper the weight of each ingot weighed at the scale:

To arrange, with the assistance of the master's porter, the ingots in the strong-hold, and put them together in pots, to be carried down to the melting-house:

To oversee the under porters in giving all proper assistance at all the weighings, and in the receipt into the mint of all bullion, and deliverance of monies or bullion:

To give the regular notices for the attendance of the officers, and other persons at the office, for business, and to do all such services as shall be directed by the master or board.

The proper duties of the Warden of the Mint are,

In conjunction with the master and comptroller, and with the assistance of the King's assayer, to make the weights of a guinea and of a shilling, according to the established standards, and also parts and multiples of the same, to be presented to council, and, if approved, to become standard weights, to be lodged in the mint:

To have the custody of the said weights at the mint, in conjunction with the master and comptroller:

To make also, in conjunction with the master and comptroller, and with the assistance of the King's assayer, copies or duplicates of the said weights, to be lodged with an officer called the stamper of money weights:

To summons once, or oftener, in every year, by warrant under the hands of himself, the master and comptroller; the stamper of money weights to appear before them, and produce the said duplicates of the standard weights, to be examined and compared with the standard weights lodged at the mint office in their custody:

To pay the salary allowed to the stamper of money weights out of monies to be entrusted to him for that service by the master of the mint:

No person to be appointed to act as deputy to the warden, without the sanction of the Lords of the Treasury.

The proper duties of the Stamper of Money Weights are,

To attend the summons of the warden, master, and comptroller, and to have the duplicate weights in his possession compared with the standard weights at the office, at least once a-year:

To adjust the duplicate weights by the said standard weights, that all weights for weighing gold and silver money may be regulated by the said duplicates:

To stamp the weights made use of in weighing

Coinage. the money, receiving a fee of one penny on every twelve weights stamped or marked pursuant to act of Parliament:

No other weights but those stamped by the stamper of weights, to be accepted by law, for determining the weight of the coins; and persons counterfeiting the stamps, or altering weights so stamped, to be fined and imprisoned:

Not to interfere with the weights of the founders' company, if they have their weights sized and marked as above:

To receive the salary allowed to his office from the warden or his deputy.

The proper duties of the Solicitor of the Mint are,

To attend the board of mint officers every Wednesday, or such other day as may be appointed, to lay before them such information and depositions, in regard to persons offending against the laws relating to coin, and to receive the board's orders for acting thereupon:

To act in conformity to such order, in the prosecution of all such persons as shall clip, counterfeit, melt down, wash, file, or diminish the current coin of the kingdom, or alter any counterfeit coin, knowing the same to be counterfeit, or be guilty of any crime or offence concerning the said coin or money, or against the laws relating to them:

For the better carrying on of the prosecutions that may happen, at the same time, in different counties, to substitute and employ such other person as he shall see fit in his stead:

To make out quarterly accounts of the expences of the prosecutions, with the proper vouchers, to be examined by the board of mint officers, showing the disbursements made by him; and to make an abstract account at the end of every year, of monies received and expended, that the balance may be ascertained and the account discharged.

Annual Routine of Business at the Mint. We shall now proceed to state the regular routine of the business of the mint, when the processes of the coinage are going forward, under the various check-officers whose duties we have enumerated.

The Bank of England are the usual importers of gold bullion. When they bring a parcel of gold for coinage, say, for example, 12 ingots; on their being brought to the mint, they are deposited with the master's assay-master, and under the key of the deputy-master of the mint, where they remain until the assay-master has made an assay of every ingot separately. When he is ready to deliver the assay reports of the said bullion to the master and worker or his deputy, the importers are required to attend in the mint office of receipt, where the said assay reports are read over by the weigher and teller. The same are recorded, according to their numbers, in the journals of the master, comptroller, and master's first clerk. To render this more intelligible to our readers, we shall insert the form of an importation of gold, by way of example, and make the same into pots, for the process of melting, which immediately follows its importation. The letter B is for better, and W for worse, than standard fineness, and the figures on the left hand are the excess of fineness

above standard, and those on the right hand, the excess of alloy beyond standard gold.

Saturday, 20th September 1817.

Importation from the Governor and Company of the Bank of England, of 12 Gold Ingots for Coinage.

A mint bill is given to the importer for this bullion, testifying the weight, and fineness, and value of the several ingots, together with the day and order of the delivery into the mint. A receipt is annexed to the bill signed by the deputy-master, and witnessed by the comptroller and King's clerk. When the said bullion is delivered to the importers in the state of coin, the mint bill is received back at the same time by the deputy-master and worker.

The first clerk and melter is next required to pot the gold for melting, and the same is recorded in the pot-book as follows:

Saturday, 20th September 1817.

FIRST POT.

SECOND POT.

These pots are delivered to the melter, and placed

to the debit of his account in the books of the deputy-master, comptroller, and King's clerk.

If the melter does not immediately melt the bullion when delivered to him, it is placed in his strong-hold, to which there are two keys, one of which is kept by himself, the other by the surveyor of the meltings.

When the bullion is to be melted, the surveyor of the meltings is in attendance, and examines that the ingots correspond with the numbers recorded in the pot-book, and, when satisfied that they are correct, the ingots belonging to each pot respectively are charged into the melting-pot, and it is his duty to attend until they are melted and cast into bars, without ever leaving the melting-house.

When the betterness and the worseness of the ingots do not balance each other (as we see it does in the examples above), but when there is an excess of betterness, which requires an addition of alloy, it is calculated after the standard of 22 carats of fine gold, and 2 carats of alloy, being the English standard of gold. The alloy is weighed by the surveyor of the meltings, and put into the melting-pots in his presence. And when there is an excess of worseness, which requires an addition of fine gold to produce the standard of the coin, the same is weighed by the surveyor of the meltings, and put into the melting-pots in his presence.

The gold is melted in pots made of black lead. Those chiefly used in the royal mint are of foreign manufacture; and are less liable to break in annealing than pots of English manufacture, from their having more black lead and less clay in their composition. Before the gold is charged into the pots, the pot is placed in a furnace of 14 inches square, and 20 inches deep from the grate. It is placed on a stand usually cut from the bottom of an old pot, and is about an inch or inch and half thick. This is covered with coke dust, which makes the pot part from it when withdrawn from the furnace, when the metal is melted. To give depth to the pot, a muffle is placed upon it, which is in fact an old pot cut in two, and the wide end fitted to the mouth of the pot. The muffle is covered with the other half of the old pot, so that it is one pot inverted over another. The object of this contrivance is to give an additional depth of 4 inches of fuel above the pot, by which a more equal degree of heat is given to the melted gold, which is an object of great importance, otherwise there might not be an uniform mixture of the alloy and fine gold, which is easily effected at a proper degree of temperature. By removing the top which covers the muffle, the process of the melting can be inspected as required. The furnace is lighted by putting a little ignited charcoal over the grate, and around the melting-pot. About 4 inches of coke is put over the charcoal, leaving the door of the furnace open, and the damper, which communicates with the flue of the furnace, shut. As soon as the coke is properly ignited, the furnace may be filled to the height of the muffle with coke; and leaving the door still open, and the damper shut, the fire will gradually burn through, and not endanger the pot, by being too suddenly heated. When the

pot is heated to a bright red, the gold is charged, and generally the pot, weighing from 90 to 105 lbs. Troy, is melted in one hour. When the metal is thoroughly melted, it is well mixed or stirred, with a rod of black lead, which is heated to a bright red before putting it into the metal. The pot is then withdrawn from the furnace, by first drawing a bar of the grate (which is moveable) on each side of the pot, and forcing all the fuel into the ash pit; a pair of tongs is then made to encircle the pot, to which is attached a lever, by which the pot is lifted upon the top of the furnace. The pot is then carried, in another pair of tongs, and its contents poured into two moulds, which produce two bars of 10 inches long, 7 inches wide, and 1 inch thick. The pot is returned to the furnace, the bars that were withdrawn replaced, and the ignited fuel put round the pot, and charged with more gold. A pot, by proper treatment, may be used eight or ten times in the course of a day.

From each pot melted, two pieces or samples are cut, one from the first poured bar, the other from the second. These are put in papers, marked accordingly by the surveyor of the meltings, who delivers them wrapt up in a slip of paper, which contains the numbers of the ingots of which the pot was composed, their gross weight, with the quantity of alloy or fine gold, as it may happen, which was added in the melting. The bars of gold, after being weighed by the melter for his own satisfaction, are placed in the strong-hold, under the key of the surveyor of the meltings, until the King's assay-master has reported their standard quality. If they are found to be the proper standard, he sends a written order, authorizing them to be delivered to the moneyers, for the purpose of making coin.

When the bars are delivered to the moneyers for coinage, they are carried by the melter to the office of receipt and delivery; where they are weighed by the weigher and teller, in the presence of one of the check officers, one of the moneyers, and the melter.

The moneyer gives a receipt in the pot-book to the melter for the gold so delivered, and the same is placed to the credit of his account in the books of the deputy-master, comptroller, and King's clerk. The same process is gone through when the moneyers return the portions of the gold, commonly called scissell, which they cannot make into money, and for the weight of which the melter gives a receipt in the pot-book, which is placed to the credit of the moneyers, and debit of the melter's account.

When silver bullion is imported into the mint, it passes through the same preliminary stages that we have seen the gold pass. The weight of an ingot of silver is from 50 to 60 lbs. Troy; they are numbered, assayed, weighed before the importers, and potted for melting the same as in gold. The only difference is in the pots, weighing from 400 lbs. to 450 Troy lbs. each. The silver is reported in ozs. and dwts.; and the standard computed to that of 11 ozs. 2 dwts. of fine silver, and 18 dwts. alloy. The pots are melted under the inspection and superintendence of the surveyor of the meltings; in every respect the same as the gold, excepting that three

Coinage. samples are taken for the assay, one from the first, the middle and last poured bar of each pot.

The process of melting silver, now practised at the Royal Mint, is a recent invention, and a very great improvement. The usual mode was to melt it in black lead pots, and a considerable coinage of tokens for the bank of Ireland was performed with the meltings done in this way. The importations being entirely Spanish dollars, and the tokens of that standard, the melter could easily melt them in quantities of 60 lbs. Troy, which was done. The inconvenience of this mode was severely felt, because ingots of silver of various qualities could not be imported for coinage, from the difficulty of not being able to blend several together in one pot, so as to produce the proper standard of our money. So sensible was government of this imperfection in the mint, that, in the year 1777, Mr Alchorne, then master's assay-master, was sent to visit the mints of Paris, Rouen, Lille, and Bruxelles, and to collect information as to the arts of coining practised in those mints, and particularly the art of melting silver in large quantities. Mr Alchorne's intimate knowledge of the English mint, together with his various and extensive knowledge as a practical chemist, well fitted him for the important undertaking; and his observations on the coin and coinage of France and Flanders is exceedingly creditable to his judgment and knowledge.

It is worthy of remark, that it is on record in the books of the mint, that, in the recoinage of King William III. the pots of silver weighed 400 lbs. Troy and upwards; but every trace as to how this quantity of silver was melted is completely lost; and it is only conjectured that it was done in pots made of wrought-iron. But not a vestige of a melting furnace, fitted for such a purpose, is to be found in the Tower, nor a single record of the method practised.

In the year 1758, some trials for melting silver in wrought-iron pots took place, by means of a blast-furnace, but they were found so laborious, inconvenient, and profitless, as to cause the process to be abandoned.

In 1787, when some silver was imported into the mint for coinage, new experiments were made by the late Mr Morrison, then deputy-master and worker, and who conducted the meltings. A blast-furnace was again tried and abandoned. He next attempted to melt the silver in large black lead pots, containing from 100 to 120 lbs. Troy; but the repeated breaking of the pots, although it was attempted to guard them by outside luting, proved a great interruption to the business, and serious loss to the melter. Trial indeed was made with cast-iron pots; but these were found subject to melt, and the iron got mixed with the silver. The work too was continually stopped by the King's assayer, in consequence of the metal not being of the proper standard, it being always refined by the process of melting, and lading it with ladles from the pot.

Independent of these considerations, very great difficulty arose at the office in arranging the potting, previous to the operation. The practice pursued at the mint (in order to reduce the metal to standard),

of combining and blending the various ingots of better and inferior qualities, adding what little portion of alloy or fine metal that might be necessary to obtain accuracy, rendered it impossible, where the ingots weighed from 60 to 80 lbs. Troy, to pot them of a weight not exceeding 100 lbs. Troy. It therefore became necessary, in the first place, to reduce the larger description of ingots to a smaller size by melting, and these were again weighed into the office of receipt. Hence a double operation took place, occasioning additional labour, waste, and expence to the melter, and requiring extraordinary trouble and attendance on the part of the office. It was very obvious that this mode of conducting the silver meltings was extremely defective, and was in consequence abandoned.

The next experiments made were with a reverberatory furnace, built after the model of those used in the Lille mint. But no better success attended these trials, and the process was, as in former cases, abandoned. The imperfection here arose from the great refinement of the silver in the melting, by the oxidation of the alloy, and which the usage of the British mint does not allow the melter to supply, as in the French mints. In the French mints, as soon as the silver is in fusion, a sample is taken out and assayed, and copper is added in the proportion to the refinement of the melted silver (which is kept in fusion while the assay is making); the whole is well stirred, and immediately laded out and cast into bars.

In the years 1795 and 1798, several farther trials were made by the late Mr Morrison, who was indefatigable in his endeavours to perfect his department, with a view to attain the object so much desired,—that of melting large quantities of silver at once, without producing so much waste and refinement in the metal. In these experiments he tried three furnaces, each of a different construction; and though he was much nearer his point, there was still an imperfection, arising from the mode of dipping out the metal from the pot with ladles, which chilled the metal, and rendered the process extremely laborious and tedious.

No new experiments were made until the year 1804. Mr Morrison, having died in 1803, was succeeded in his office by his son, the present deputy-master and worker of the mint. The extreme scarcity and defective state of the silver coin at this time, arising from the defective state of the melting department, urged Mr Morrison to renew the experiments of his father. In following these experiments, Mr Morrison had in view the construction of a furnace adapted for the use of cast-iron pots,—the use of pots of a size capable of melting from 400 to 500 lbs. Troy, at one charge,—the adaptation of such machinery as would supersede the clumsy and wasteful process of lading the silver from the pots when melted,—and, lastly, the introduction of the use of moulds made of cast-iron, in place of those then used in the mint, and which were made of sand.

In all these objects Mr Morrison, highly to his credit, perfectly succeeded; and the silver melting department of the new mint was construct-

Coinage. ed according to the furnace first used in the experiments which led to such a satisfactory result. The whole has been in use since 1811, and the department is capable of melting, with ease, 10,000 lbs. Troy of silver daily; as was done for several months during the late recoinge. (1817.)

We shall now proceed to a description of the machinery and furnaces of the silver melting department, together with the mode of conducting the process.

The upper part of Plate LXI. is a perspective view of the machine, for pouring the melted silver into the ingot moulds.

Fig. 1. AA, are the furnaces in which the metal is melted. These are air-furnaces, built of fire-brick, in the usual manner of melting furnaces, but, to render them more durable, the brick-work is cased in cast-iron plates, which are put together with screws. BB are the covers to the furnace: they are held down to the top plate of the furnaces by a single screw-pin for each; and, on the opposite side of the cover, a handle a is fixed. By pushing this handle, the cover is moved sideways upon its centre-pin, so as to remove it from the furnace mouth. A roller is fitted to the cover, to run upon the top plate, and render the motion easy.

The interior figure of each furnace is circular, 30 inches deep, and 21 inches in diameter; the bottom is a grate of cast-iron bars (each bar being moveable) to admit the air. Upon the grate is placed a pedestal or stand of cast-iron, of a concave shape, covered an inch thick with coke or charcoal dust, and upon which the pot is placed in which the silver is melted. The pedestal is nearly two inches thick, and is fully two inches broader in its diameter than the pot, the object of which is to protect the hip of the pot from the very high heat which the current of air ascending through the grate, when the furnace is at work, creates, and which would otherwise melt the pot. This precaution is essentially necessary, from the pedestal raising the pot so considerably above the grate, and from its being entirely surrounded by the fire in the furnace. If the furnace, however, is properly managed, there is no risk of melting the pot. On the top or mouth of the pot is placed a muffle, which is a ring of cast-iron, six inches deep, made to fit neatly into the mouth of the pot; the use of this muffle is similar to that used in melting gold, to give a greater depth of fuel in the furnace than the mere length of the pot, and which gives a greater degree of perfection to the process. The muffle is also extremely convenient, by giving a depth to the pot, if we may so speak, which enables ingots of silver to be charged, which are longer than the depth of the interior of the pot. The top of the ring or muffle is covered with a plate of cast-iron, to prevent the fuel from falling into the pot, and secure the metal from the action of the atmospheric air when in fusion. Each furnace has a flue 9 inches wide and 6 inches deep. The flue is 4 inches from the top of the furnace, and proceeds in a horizontal direction, and extends to the flue C, which is 9 inches square, and is carried up in a sloping direction

to the stack or chimney, which is 45 feet high from the grate of the furnace.

Coinage. When the furnace doors, BB, are closed, the current of air which enters at the grate ascends through the body of the furnace, and causes the fuel, which is coke, and which surrounds the melting pot, to burn very intensely. The degree of heat wanted, however, is very nicely regulated by a damper, which is fixed in the flue of each furnace, and exactly fitting the square of the flue, so that any portion of draught can be given to the furnace that may be wanted. The damper is a plate of wrought iron, fixed in a frame, and is easily moved in and out, so as to increase or diminish the size of the flue. It is fixed in the brick work of the sloping flue C, about 18 inches above the top of the furnace. The furnace doors B have small holes in them to look into the furnace; these are closed by stoppers or plugs of cast-iron.

When the furnace is put to work, it is lighted by some ignited charcoal being put upon the grate, and around the pot (for the pot is always in its place before the fire is lighted); upon the charcoal about three inches deep of coke is put—the door B is shut, and the damper is pulled out about two inches. When the coke is ignited, a similar quantity is put on, and so continued until the furnace is filled with ignited coke. The object of this precaution is to prevent the cracking of the cast-iron pot by being too suddenly heated—and it is generally about two hours before the pot can be brought to a charging heat, to do it with perfect safety. Before the silver is charged the pot is heated a bright red; it is then examined to see if it has cracked in bringing up, as it is technically called. This is done by placing a cold iron tool of considerable thickness in the centre of the pot, which immediately renders any crack visible to the eye. When satisfied that the pot is sound the silver is charged into the pot. With the silver is put into the pot a small quantity of coarsely grained charcoal powder, which coats the inner surface of the pot, and prevents the silver from adhering to it. When the silver is brought to the fusing point, the quantity of charcoal is increased until it is nearly half an inch deep on the surface of the silver, and which keeps the silver as much as possible from the action of the common air, and prevents that destruction of the alloy which would otherwise cause a considerable refinement in the metal. When the silver is completely and properly melted, it is well stirred with an iron stirrer, so as to make the whole mass of one uniform standard quality. The pot is then taken out of the furnace by the crane and conveyed to the pouring machine, by which its contents are poured into the ingot moulds.

Fig. 3. is the crane; it is supported by a strong column of cast-iron X, which is firmly fixed in masonry beneath the floor. The gibet of the crane marked WY is cast in one piece; it has a collar at e which fits upon a pivot formed at the upper end of the column X. At the lower part of the gibet is a collar which embraces the column near its base. On these two supports the gibet turns freely round, so that its extremity W may be placed over either of the

Coinage. furnaces BB. The wheel-work of the crane is supported in two frames zz, which are fixed to the gib by three bolts; it consists of a cog-wheel c, upon the end of the barrel, on which the chain winds, and a pinion b, which gives motion to the cog-wheel. The axis of the pinion has a winch or handle (a) at each end to turn it round. The chain d, from the barrel, is carried up over the pulley at c, which is fitted in a part of the gib immediately over the pivot at the top of the column X. The chain then passes over the pulley W at the end of the gib, and has the tongs VT suspended to it. These are adapted to take up the pot between the hooks or claws T, at the lower ends. The two limbs are united by a joint like shears, and the upper ends V, are connected with the great chain by a few links. The pot has a projecting rim round the edge, and the tongs take this rim to lift the pot out of the furnace. The pot being wound up to the required height, by turning the handle a; the gib of the crane is swung round to bring the pot over the pouring machine, and it is lowered down into it, for the convenience of swinging the crane round a worm, which is fixed upon the column X at O, and a worm or endless screw is mounted in the frame z to work in the teeth of the wheel. The screw being turned by a winch on the end of its spindle will cause the gib to move round on the column.

Fig. 2. represents that part of the pouring machine in which the pot is placed. M is an axis which is mounted in the frame of fig. 1. by the pivots at its ends. To this axis is fixed a cradle, which receives the pot. The cradle is jointed together so as to open and shut, and the screw m draws the parts together until they will fit. The pot L is an arched rack, forming a continuation of the principal bars of the cradle. When the cradle is in its place, as in fig. 1. the rack L is engaged by a pinion K, and can thereby be elevated so as to pour out the metal at a lip or spout which is made in the edge of the pot for that purpose. The axis of the pinion K is turned by means of a winch D with a train of wheels DE, FG, and HI. The man who turns this winch stands before the pot, so as to see what he is doing. The frame of the pouring machine is sufficiently evident from the figure. It is so made as to leave an open space beneath for the carriage containing the ingot moulds.

Fig. 4. is a separate view of a pair of ingot moulds. The two parts R and S put together, and form a complete mould, as shown in fig. 5. The upper edge or mouth is a little enlarged to facilitate the pouring of the metal. The moulds are made of cast-iron. The part R has the bottom and one side formed on it, and the other half S has one side formed on it. Before the moulds are used, they are heated in an iron closet, which has flues surrounding it, and they are then rubbed on the inside with linseed oil.

PQ, fig. 1. is the carriage into which a row of these moulds are placed, as shown at 4, and they are screwed up close by two screws pp, so as to hold them tight; the moulds rest upon a plate, which is suspended by screws q, at each end, and can by that means be raised or lowered to suit different heights of moulds. The carriage is supported on four wheels QQ, which run upon a railway. PP is a rack fixed

to the bottom plate of the carriage; in this rack a cog-wheel N, acts; the cog-wheel is turned by a pinion which has a handle O, fixed upon it; by turning the handle the carriage is moved along upon the rail-way; and any one of the moulds 4, can be brought under the spout of the pot 2; then, by turning the handle D, the pot can be inclined so as to pour the metal into the mould until it is full.

In the silver melting-house there are eight melting furnaces, two cranes, and two pouring machines. Each crane stands in the centre of four furnaces, freely commanding the centre of each, and conveys the pots to the pouring machine. The eight furnaces are worked three times daily, and each pot contains, upon an average, 420 lbs. Troy, making the total melting 10,080 lbs. There are four men to each four furnaces; each party pour their own pots, and the whole meltings are finished from the time of first charging in the morning, in little more than ten hours.

The whole of the silver meltings, as we before observed, are conducted under the superintendence of the surveyor of the meltings; and he allows no silver to be delivered to the company of moneyers by the melter, unless he has a written order from the King's assayer master, authorizing such delivery.

The meltings are performed by contract with the master of the mint and his first clerk, as melter. He is responsible to the master for all the bullion he receives, and delivers weight for weight, which renders his situation one of considerable risk and great responsibility. He also finds security for the due performance of the duties of his office.

The bars of silver, of the approved standard, are delivered over to the moneyers, in the same manner as we have detailed respecting gold. The moneyers also perform the various processes of the coinage under contract with the master of the mint, always delivering weight for weight. They also give security for the due performance of the duties of their office.

The first process to which the silver bars are subjected, is that of flattening, rolling, or laminating, in the rolling mill. The bars, before they are put through the rollers, are heated to redness, which makes them much easier rolled. They are heated in a reverberatory furnace.

When the gold bars are subjected to the same process, they are rolled cold, and a bar of an inch thick can be reduced to the thickness of a half sovereign without ever being annealed, and could be reduced much thinner if necessary, and not show the least symptom of cracking.

Fig. 6. is an elevation of one pair of rollers, and the wheel work for giving motion to them. A is the upper and B the lower roller; CC are the standards of the cast-iron frame which supports them. Each of these standards has an opening in it to receive the bearing brasses for the pivots of the rollers. The upper roller is suspended in brasses which are regulated by the large screws FF, which admit of placing the rollers at a greater or less distance asunder. This is shown by the separate figure of one of the screws; hh are the brasses, and k the hole to receive the pivot of the roller. On the upper part of the screw a collar f is fitted, and from this two bolts gg de-

scend, and are fastened to the brasses hh, with nuts beneath. By these the roller is suspended, but, by turning the screw round, the brasses rise or fall. The brasses hh are fitted very accurately into the grooves on openings in the standards CC.

For the convenience of turning both screws round together, each has a cog-wheel F fixed on the upper end of it. These are turned by two worms HH, fixed on a common axis, which has a handle G in front. See the plan, fig. 8. By turning this handle the upper roller is either raised or lowered, as is required, but will always be parallel to the lower one. The two standards CC, are firmly bolted down to the ground sills DD, which are of cast-iron, and are bedded in the masonry EE. The standards are farther united by bolts a. At the upper part S, is a cross bar fixed between the standards, to support a small table or platform, on which the metal is placed when it is to be presented to the rollers.

The rollers are put in motion by a steam-engine. The crank of the engine has a cog-wheel upon it which turns a pinion. Upon the axis of this is a very heavy fly-wheel, which turns with great velocity. On the end of the same axis, is a pinion which turns a large wheel M, and this gives motion to a long shaft NN, which extends beneath the rollers, and is continued a sufficient distance in the same direction, to turn two pair of rollers, one of which only are represented in the drawing. At L, a wheel is fixed on this shaft, to turn the upper roller A, by means of a wheel K, which is supported in the standards kk, and its axis is connected with a short shaft rr, with the square on the end of the roller A. rr Are the sockets by which the shafts are joined, and they admit of a little yielding when the roller is raised.

The wheel O, is fixed on the shaft N, to turn the lower roller B, by means of the wheel P; but the wheels P and O do not touch, being of smaller diameters, and an intermediate wheel is applied on one side, so that its teeth engage with both the wheels O and P; by this means the two rollers A and B are made to turn round in opposite directions, and then their adjacent surfaces will move together. The wheel P is supported in standards pp, and its axis R is connected by a shaft Q, with the lower roller B.

Fig. 7. is a gauge so ascertain the thickness of the plates, which are reduced by the operation of the rollers; it consists of two steel rulers, fixed fast together at one end, and the other end is a certain distance asunder, forming an opening between them, which gradually diminishes to nothing. The sides of the rulers are divided. In using this gauge to determine the thickness of a piece of plate, the edge of the plate is applied to the opening between the rulers, and the divisions of the rulers show the distance it will go into the opening before it fits tight, and the thickness is ascertained by the number of the divisions.

Plate LXIII., figs. 3. and 4., represent the machine by which the plates of metal from the rolling-mill are cut into slips of a convenient width, for cutting out the circular pieces or blanks, which are to form the coin. This width is generally that of 2 crowns, 2½ crowns, shillings, &c.

LL is a strong iron frame, which is screwed down to the ground sills of the mill, so that the cog-wheel D will be immediately over the shaft which turns the rolling-mill, and can be turned by a cog-wheel upon that shaft. The cog-wheel D is fixed upon an horizontal axis BB, which is supported in the frame LL. AA is a similar axis placed at the top of the frame, and turned round by a cog-wheel C, which engages with the wheel D. On the extreme end of each axis A and B, a wheel or circular cutters E and F is fixed. The edges of these cutters lie in close contact laterally, and overlap each other a little. The edges of the cutters are made of steel hardened, and they are turned very truly circular, and the edges which overlap are made very true and square. Whilst they are turning round, if the edge of a plate of metal is presented to them, it will be cut or divided just in the same manner as a pair of shears. H is a narrow shelf, upon which the plate is supported when it is pushed forwards to be cut, and G is a guide fixed upon the shelf; the edge of the plate of metal is applied against this guide, whilst it is moved forwards to the cutters. The guide is moveable, and the distance which it stands back from the cutting edges, or line of contact of the two cutters, EF, determines the breadth of the slip of metal which will be cut off.

To give these slips of metal the exact thickness which is requisite before they are cut up into blocks, they are subjected to a more delicate rolling; or they are drawn between dies by a machine, invented by Mr Barton, the present comptroller of the mint.

Fig. 7. Plate LXIII. represents the finishing rollers, viewed at the end of the frame, in order to show the manner of adjusting them; for it is only in those parts that they differ from the great rollers: a is one of the pivots or centres of the upper roller; it is accurately fitted in a collar of brasses, which collar is held down in a cell at the top of the standard by a cap d, with two bolts and nuts. These are not intended for the adjustment of the rollers as in the former instance, but the lower roller is moved for this purpose. The pivot b, of the lower roller, is received in a brass bearing, which is moveable, in the opening in the standard frame. The brass rests upon a wedge, e, which is fitted in a cross mortice through the standard. By forcing the wedge farther in the brass of the lower roller, it will be moved nearer to the upper roller. The standard at the other end of the rollers is made in the same manner, and the wedges of both must be moved at the same time. To give them motion, a screw, f, is fitted into each wedge, and upon these screws are worm wheels, g, which are both moved by worms cut upon an horizontal axis, then extends across from one side of the frame to the other, and has a handle at the end to turn it round by, and move the screws and wedges both in equal quantity; l is the table on which the metal is laid to present it to the rollers.

Plate LXII. contains drawings of Mr Barton's new machine for drawing the slips of metal between dies, by which a greater degree of accuracy is obtained in the thickness of the metal; the operation is similar to wire drawing.

Figs. 1. 2. and 3. represents a small machine for

Coinage. thinning the ends of the slips of metal, so that they will enter into the dies, through which the whole of the slip is to be drawn. It is a small pair of rollers, which are shown on a large scale, in fig. 1.; A is the upper roller, and B the lower: this has three flat sides, as represented; C is the slip of metal put between the rollers; D is a stop adjustable in the line of the motion of the slip of metal C. Fig. 2. is an end view, and fig. 3. a side view of the frame or machine in which the rollers are mounted. AB are the rollers, which are made to turn round together by pinions a b. F is a large cog-wheel, which is fixed on the end of the axis of the lower roller. This cog-wheel is turned by a pinion G, which is fixed on an axis extended across the machine, and having a fly-wheel fixed on one end, and at the other a drum H, to receive an endless strap, by which the machine is put in motion; a crank is formed on the middle of this axis, and a rod d, is joined to the crank, to connect it with the moving blade K of a pair of shears, of which the other blade L is fixed to the frame. The distance of the rollers is regulated by a screw ee, at the top of each standard. These screws have pinions at the top of them, and are turned round by a pinion which is placed between them, and engages the teeth of both pinions, so as to give motion to the two screws at the same time, when the middle wheel is turned round by a cross handle which is fixed to the top of it. If the slips of metal which are to be put in this machine are not exactly square at the ends, they are cut off smooth and square by the shears, which keep constantly moving; the end of the slip is then presented between the rollers, not on that side which would draw them in between the rollers, as in common rolling, but on the opposite side; when one of the flat sides of the lower roller comes opposite to the upper roller, then the piece of metal can be pushed forwards between the two, until the end stops against the stop D, as in fig. 1.; then as the rollers turn round, and the flat side of the lower roller passed by, the cylindrical parts of the roller will take the metal between, and roll it thinner at the end which is between the stops and the point of contact of the rollers.

Fig. 5. is a perspective view of the drawing machine at work.

Fig. 7. and 8. a section to show how the slip of metal C is drawn between the dies by the tongs, fig. 7.

Fig. 4. is a section of the steel dies. They are two cylinders AB of steel, made very hard and extremely true; these are fitted into two sliders DD, and are held fast by clamp pieces EE screwed against them. The steel cylinders are very accurately fitted into their beds in the slides, so that the steel shall be firmly supported and prevented from bending or turning round, and presenting but a small portion of their circumference against the slip of metal. The sliders D are fitted into a box, fig. 8. and 9.; they fit flat on the bottom of the box, and two clamps FF are screwed against the sliders to confine them to the box. The lower slider is supported by two screws ff, and the upper slider is forced down by a large screw G; this has a cog-wheel fixed on the top of it, with a pinion and lever to turn the screws round very slowly, and

regulate the distance between the dies. H is a clamping nut, fitted upon the screw, to take off all possibility of shake; the sliders are also bound fast sideways by screws tapped through the sides of the box, the points of which press upon steel plates between them and the sliders. In order to render the contact between the points of the screws, supporting the under slider and the point of the adjusting screw, forcing the upper slider, still more complete, two extending screws are introduced at the ends of the steel dies between the sliders, by which a sufficient degree of contact, to overcome the spring of the materials, may be excited before the dies come into action on the slip of the metal.

Coinage. The box of dies is fixed at one end of a long frame, as is shown in fig. 5. This frame supports two axes, AA, one at each end. Upon these axes wheels are fixed to receive endless chains, BB, which move along a sort of trough or railway, formed on the top of the frame. The chains are kept in motion by a cog-wheel C, which is fixed upon the axis most remote from the box of dies. This cog-wheel is turned by a pinion D, on the axis of which is a wheel E, and this wheel is turned by a pinion F, on the axis of the drum G, which is moved by an endless band proceeding from some of the wheels in the mill, and which is thrown in and out of gear at pleasure by a tightening roller. The slip of metal is drawn through the dies by the chain, with a pair of tongs, fig. 6. and 7. ab are the two jaws of the tongs which are united with each other by the joint pin c. This has a small roller or wheel fitted on each end to run upon the railway on the top of the frame; dd are a similar pair of wheels, the axle of which is connected with two links ee; this axle passes between the tails of the tongs, but is not fixed to them. The ends of the links have a double hook formed on them as shown at fig. 7. The tongs run upon their wheels immediately over the endless chain, so that when the end f of the links ee is pressed down, one of the hooks catches on a cross pin of the chain, as in fig. 7. The axle of the wheels dd, acting between the inclined parts of the tails of the tongs, tends to throw them asunder, and, at the same time, the jaws of the tongs bite with very great force; the links ee draw the tongs along with the chain BB. The links are carried a long way beyond the axle of the wheels, and have a sufficient weight h fastened to them, which will lift up the hooked end f, and disengage it from the chain, except when there is a considerable strain on the tongs.

To use this machine, a boy takes hold of the tongs by the handle r, when they are disengaged from the chain, and pushes the tongs forward towards the box of dies. The tongs run freely upon their wheels, and the jaws open when moved in that direction, because two small pins ii are fixed across between the links, and acting on the outsides of the tails of the tongs, close them together, and this at the same time opens the jaws. The tongs are pushed up close to the box of dies, and the jaws enter into a recess N, fig. 8. which is formed for that purpose. Another boy takes a slip of metal, which is previously made thin by the rollers, fig. 1., and introduces it between the dies, and also between the

jaws of the tongs, which are open. The boy who holds the tongs now takes the handle s, which is fixed on the back of the tongs, and holds it fast, whilst with the other hand he draws the handle r, at the end of the links, away from the tongs. This has the effect of closing the jaws of the tongs upon the slip of metal between them; at the same time he depresses the handle r, and the hook at the end of the links ee will be caught by the first cross pin of the chain, which comes beneath them. This puts the tongs in motion, but the first action is to close the jaws and bite the piece of metal with great force, in consequence of the axle-tree of the wheels being placed between the inclined planes of the tongs. When the tongs have closed on the metal, with all their force, they move with the chain, and draw the slips of metal through the dies, which operating upon the thicker parts of the slip with greater effect than upon the thin, reduces the whole to an equable thickness. When the whole length is drawn through, the strain upon the tongs is instantly released; and the weight lifting up the hook at the other end of the links, they are ready to be advanced again to the dies, to draw another bar. The frame, fig. 5, contains two pair of dies, and the same wheel serves for both. At the mint are two machines like that shown in fig. 5. They are placed side by side, with a sufficient space for the boys to work between them.

These machines were made by Mr Maudslay, under the directions of the inventor.

The slips of metal produced from this machine are considerably more uniform in thickness than when finished at the adjusting rollers; consequently the individual pieces are made more nearly to the standard weight, which was the object in view by this invention. This has become a point of great importance in the practice of the mint, from the remedy on gold in weight being reduced from 40 to 12 Troy grains. When the pieces cut from slips of metal prepared by the drawing-machine are pounded and weighed, which is telling the number of pieces in a pound Troy, sovereigns or half-sovereigns, the variations from standard either way seldom exceed 3 grains Troy. It is reckoned good work from the adjusting rollers when the variations are under 6 Troy grains.

The plates of metal, prepared by the adjusting rollers or the drawing machine, are cut out into circular pieces nearly of the size of the intended coin. This is done by the cutting out press, fig. 1. Plate LXIII. CCCC is a cast-iron frame which is fixed on a stone basement. E is the screw which is fitted through the top of the frame and actuates a slider F. At the lower end of the slider a steel punch a, is fixed. Its diameter is exactly equal to that of the pieces which are to be cut out, c is the steel die, which has a hole in it of a proper size to fit the steel punch; d is a box with screws for adjusting the die, so that the hole in it will be exactly beneath the punch.

The slider F is fitted into a socket G, which guides it so that it will descend correctly into the hole in the die. b is a piece of iron which is fixed a small distance above the die c; it has a hole through to admit the punch. Its use is to hold down the piece of

metal when the punch rises, otherwise the piece would stick to the punch. Coinage.

On the upper end of the screw a piece Q is fixed, and an arm projects from it with a weight P at the end; and it is this weight which gives the necessary momentum to punch out the piece. D is a spindle fixed upon the piece Q in the line of the screw; it is supported in a collar A, at the upper end, and above the collar a lever DGF is fixed; at one extremity of this lever a roller F is fixed, and this is acted upon by projecting teeth, which are fixed in the rim of a large horizontal wheel, which is turned round by the power of the mill. This action is explained by fig. 2, which is an horizontal plan of the upper part of the axis. SS is part of the rim of the large wheel, and T one of the projecting cogs, which, when the wheel turns in the direction of the arrow, will take the roller F, at the end of the lever FD, and turn the lever round in that direction, which will wind up the screw and raise the punch out of the die. Also this action draws a rod H, which is connected with the lever by a joint; the other end of this rod is connected with a bended lever, from the other arm of which a rod descends and has a piston fixed to it. This piston is fitted into a close cylinder; hence, when the piston is drawn up, it makes a vacuum in the cylinder, and the pressure of the atmosphere on the piston causes a reaction, and the instant that the roller F escapes or slips off from the tooth T, the reaction of the piston draws the joint H back, and makes the screw turn round in that direction, which causes the punch to descend into the die, and it will pierce out a piece from a plate of silver or gold which is laid upon the die, which piece will be exactly the size of the punch, which, as before mentioned, is the same as the intended piece of money. When the machine requires to be stopped, a catch K, is suffered to rise up and hook the lever G, so that it cannot return by the action of the exhausted cylinder and pierce the plate. This catch is shown in fig. 8. At K it is moveable on a joint l, and is thrown upwards by a spring k. To this spring a cord O is fastened, and the lower end of the cord has a traddle fastened to it. The boy who applies the plates of metal to this machine places his foot upon the traddle, and draws down the spring and the catch K, and then the machine will make a cut every time that a cog T of the great wheel S passes by; but if the boy relieves the traddle, then the spring K lifts up the catch k, as in fig. 8., and when the end of the lever G comes over the catch, it will be caught thereby, and held fast from returning by the action of the exhausted cylinder. The joint l of the catch K is made at the top of a long lever IN, of which m is the centre pin, when the lever G is detained by the catch K; if the end N of the lever is drawn towards fig. 1. it draws the lever G still farther, so that the roller F will be raised quite clear of the tooth T of the great wheel, and prevents any unnecessary wear of the machinery when the process is stopped.

Twelve of the cutting-out presses, fig. 1, are arranged in a circle round the great wheel SS, which is turned by a steam-engine, and has a large fly-wheel fixed upon the same axis, just above

Coinage. the wheel S, to regulate the motion. The stone basement on which the presses are fixed is circular, and the bearing A are all fixed in a circular iron frame, which is erected upon the stone basement by an iron column placed between each press. The whole forms a very handsome colonnade, and is placed in the centre of a circular room, which is lighted by a sky-light in the dome. The air-cylinders are concealed within hollow pilasters, which ornament the walls of the room, and appear to support the dome. The rod H is jointed to a piece h, which is fitted to slide upon the lever FG, and is moved by the screw I, so as to be fixed at any required distance from the centre, and give a greater or lesser effect to the reaction of the exhausted cylinder. R, fig. 1. is a strong wooden spring, against which the balance weight P strikes to stop its motion, when it has made its required stroke to pierce the plate.

This cutting-out machine was invented by the celebrated Matthew Boulton of Soho, who had a patent for it in 1790, and prepared it at that time for working the coining or striking presses, but having invented a better method of working the latter, he confined this plan to the smaller presses for cutting out the blanks.

The blanks after being cut out by the last mentioned machine, are carried to the sizing-room, where each individual piece is adjusted to its standard weight. The light pieces are selected for remelting; and the heavy ones, if not considerably beyond weight, are reduced to their standard weight by rasping their surfaces with a coarse rasp or file. The superior accuracy of Mr Barton's beautiful machine has considerably abridged the labour of this inelegant and unmechanical process.

The pieces thus adjusted, are in a state of great hardness from compression by the rolling and drawing processes, and by which, in fact, their latent heat has been squeezed out. They attain their softness again by being heated to a cherry red heat in a reverberatory furnace; after which, they are boiled in very weak sulphuric acid, which makes them very clean, and of a very white colour. When dried, either in warm sawdust, or over a very slow fire, they are in a state for the two next processes, which are the milling, and the coining or stamping.

Operation of Milling. The operation of milling is to be performed round the edge, to prevent their being clipped or filed (which was a fraud commonly practised upon the ancient money made before the introduction of milling or lettering round the edge). The construction of the milling-machine will be easily understood from the inspection of fig. 5. and 6. Plate LXIII.; fig. 5. being an elevation, and fig. 6. a plan of the same. The parts which operate upon the piece of money, consist of two steel bars or rulers, dd and ee, the adjacent edges of which are cut or fluted. The bar ee is immovable, being fastened down by two clamps hh to a cast-iron plate DD, forming the base of the whole machine; the other bar dd is prevented from rising by the pieces gg, but has the liberty of moving backwards and forwards in the direction of its length, and is guided in such motion by laying half its thickness in a groove formed in the plate DD. A rack CC is

fixed to the moving ruler, which engages in the teeth of the wheel B, mounted on an axis lying across at right angles to the ruler, and supported at its ends by two standards rising up from the Plate DD. On one end of the axis, a handle is fixed for giving motion to the machine. Two blanks are put into the machine at the same time, as shown at fig. 6., and the ruler ee can be made to approach nearer or recede further from the ruler dd by the two screws ff, to take in a different sized piece between them. The operation of the machine is very simple. Two blanks being placed between the edges of the rulers, the handle A is turned round half a turn, which moves the ruler dd endways, sufficient to mark the blank all round the edge. The two milled pieces are then taken out, and two other blanks are placed between the rulers; the handle A being turned half round in an opposite direction, carries the ruler dd back again to the position in which it first stood: thus two more blanks are milled, and so on. The machine is placed upon a strong wooden bench, to raise it to a convenient height for the man who turns the handle; the blanks are placed in the machine by a boy who is stationed on the opposite side to that where the handle is.

Plate LXIV. is the coining-press, which stamps the money. Fig. 1. is an elevation of the press; CCB is a strong cast-iron frame, which is firmly screwed down upon a stone basement by the screws cc; the upper part B is perforated perpendicularly to receive the screw DD. One of the steel dies which strike the coin, is fixed to the lower end of this screw by a box, 4, and the other die is fixed in a box, 6, which is fastened down upon the base of the press. The heavy balance weights RR, are fixed on the top of the screw, which, being turned round, presses the upper die down upon the blank piece of coin which is laid upon the lower die and gives the impression, a sufficient force being obtained from the momentum of the loaded arms RR. The motion is communicated to the screw by a piece A, which ascends to the ceiling of the coining-room, and is worked by a steam-engine, with machinery, in the apartment in the room over the coining room.

Eight presses, similar to No. 1., are placed in a row upon the stone basement, and very strong oak pillars are erected upon the basement, and reach to the ceiling. Each press is contained between four such pillars, and iron braces are fixed horizontally from one pillar to another on the opposite side. These braces support blocks of wood against which the ends RR of the arms strike, to stop them from moving farther than necessary, as, without such precaution, the hard steel dies would sometimes come in contact and be broken. The piece of blank coin is contained within a steel ring or collar, whilst it is stamped, and this preserves its circular figure. The ring is shown at a large size at W, in fig. 5. V is a three-pronged spring which always bears the spring upwards; the opening through the ring W is made to fit upon the neck of the lower die T, fig. 6. When the ring is dropped upon the neck of the die, the upper surface of the ring and of the die will be in one plane. The ring admits of being raised up up-

on the neck, and will then form a recess or cell, which is just adapted to receive a piece of money. The collar W is made to rise and fall upon the neck of the die by means of the levers GG, fig. 5.; these are fitted upon centre pins or joints in a large ring gg, which is placed on the outside of the box, fig. 6., containing the lower die T, and is fixed fast upon it, as shown at 5 and 6, fig. 1., by clamping the screws gg. The levers GG are forked at the outer ends to admit studs at the lower ends of iron rods EE, which rise up through holes in the solid metal of the press, and are united to a collar G, fitted on the upper part of the screw D. When the screw of the press is turned back, and the upper die is raised up, the rods raise the outside ends of the short levers G, and the inside ends depress the ring; a blank piece of money is laid upon the die, and when the screw is turned to bring the upper die down upon it, ready to stamp the impression, the levers G are released, and the triple spring V lifts the collar up, so that it surrounds the piece of money; and in this state the blow is struck. Immediately after the press returns by its recoil, and then the levers G force the collar down upon the neck of the die, and leave the piece free. The lower die is fixed in a box, fig. 6., by four screws tt, which admit of adjusting it with precision beneath the upper die. The box, fig. 6., is screwed down upon the base of the press by four screws. The upper die is shown at S, fig. 3., which explains how it is fastened to the screw; vv are four screws, by which the die is held in a box, fig. 3. The box is fitted into a ring or collar, as shown by the dotted lines, F: see also fig. 1. The arms of the collar F are attached to the rods EE, by two nuts at each end, and this makes the collar F and the box S always follow the screw, and keep a close contact with the end of the screw, which enters into a cell in the top of the box, fig. 3., but leaves the screw at liberty to turn round independently of the box.

Fig. 2. is a ring which is fastened by its screws, ww to the screw of the press; a claw V, descends from the ring, and enters into cavity o, in the edge of the box, fig. 3., which cavity is near three times as wide as the claw V, and therefore allows the screw to turn round for a certain distance without turning the box, fig. 3., but beyond the limits of this motion the screw and die will turn round together. The intention of this is to press the upper die down upon the coin with a twisting or screwing motion; but if the die was to rise up with a similar motion, it would abrade and destroy the fine impression; for this reason the notch o, is so wide as to allow the screw to return, and raise the die from immediate contact with the coin, before it shall begin to turn round with the same motion as the screw.

Fig. 4. is a box which is screwed over the box for the upper die, as shown in fig. 1., in order to keep the upper die firm in its cell.

The great screw of the press is made cylindrical at the upper and lower ends, where it is seen at DD, fig. 1., and these ends are accurately fitted in collars, which are bound tight by the screws aa; the real screw or worm, part concealed within the solid metal B, and has no other office than to force the

die down, the guidance laterally being effected by the collars aa.

It now remains to show how the press is made to remove every piece of money which it strikes, and to feed itself with a fresh blank piece.

Fig. 1. HIK, is a lever, of which I is the fulcrum; it is supported on a bar Q, fixed vertically from the cheek of the press, and steadied by a brace h. The upper end of the lever is actuated by a sector 7, see fig. 7., which is fixed upon the screw D. When the screw turns round, the groove in the sector being of a spiral curve, will move the end H of the lever to and from the screw; and the lower end K of the lever being longer, it moves a considerable distance to and from the centre of the press. b Is a socket or groove in a piece of metal, which is fixed to the perpendicular bar Q, and the upper end of the lever H is guided in this groove, to prevent any lateral deviation.

The lever K gives motion to a slider L, fig. 8., which is supported in a socket O, screwed against the inside cheek of the press, and the slider L is directed exactly to the centre of the press, and on the level of the upper surface of the die.

Figs. 8, 9, and 10. represent three views of the slider and socket; NMO is a kind of trough or socket in which the slider runs; this slider is formed of two pieces hollowed out on the sides, which are put together, and the two pieces are held together by screws. O is the part by which the socket is fastened to the press. The slider is a thin steel plate p, see also fig. 10.; it is made in two pieces, P and p, which are united by the joint q. The extreme end is made with a circular cavity; and, when the two limbs shut together as represented, they will grasp a piece of money between them, and hold it by the edge; but, if the limbs are separated, the piece will drop out. The limb p of the slider is opened or shut by the same movement which moves the slider endways in its socket. Thus a plate L is applied flat beneath the socket N, and has an edge turning up and applying to the upright edge of the socket. A pin is fixed into this edge, and is embraced by the fork at the lower end of the lever k, fig. 1. By this means the sliding piece L is made to move on the outside of the socket N. It is kept in its place by a fillet k, fig. 9., which is screwed to the upright edge of L, and the fillet enters a groove formed along the upper surface of the socket N.

The sliding piece L is made to move the steel slider within the socket by means of three studs, which project upwards from the bottom plate of L, fig. 10., at rrs, and pass through grooves in the bottom plate of the slider, so as to act upon the steel slider P, in the manner shown fig. 10. The left hand piece r is received into an opening in the middle of the slider P, fig. 10. The other two studs r and s include the shank of the limb p between them, and these studs are cut inclined, so that, when the piece L is moved to the right, the studs rs will close the limb p until they are shut, and then the studs will carry the slider forward; but, if the sliding piece L is moved to the left, its studs will first close the limbs, and will then draw back the slider. On the top of the socket N a tube M is placed, and it is filled with blank pieces of coin; the

Coinage. tube is open at the bottom to the slider, and the pieces rest upon it. When the screw of the press is screwed down, the slider P draws back to its farthest extent, and the circle formed at the end between its limbs comes exactly beneath the tube M; the limbs being open, a blank piece of coin drops down into the circle of the slider, then the screw of the press, in returning, moves the lever HIK and the piece L; this acts by its studs upon the moveable limb p, and closes it upon the blank piece; the studs having now found a reaction, push the slider P forwards in its socket, and carry the piece forward upon the die, as shown in fig. 1., and which will push off the piece last struck. The screw having now arrived at its highest position, begins to descend, and the slider L to return; but the first action of the studs of the sliding piece L is to open the limb p, and then the slider withdraws, leaving the piece of money placed upon the die. As the screw of the press descends, the ring W, fig. 5., rises up to enclose the piece as before mentioned, whilst it receives the stroke, and the slider P at the same time returns to take another piece from the tube M in the same manner as before described.

Fig. 11. is a section to show the manner of mounting the lower die for a coining press. This is used in the French mint. V is a piece of metal or box, as it is placed upon the base of the press, and held down by a ring with screws t; this holds it fast, but admits of lateral adjustment. In the top of the box is a hemispherical cavity to receive the hemisphere W; the upper side is flat, and the die T is placed upon it, to hold the die down; it has a small projecting rim at the lower edge, and a rim X is screwed upon the outer edge of the box V, and binds the die down. The object of this plan is, that the die may always bear fairly to the money which is to strike.

Figs. 12. and 13. is a divided collar invented by Mr Droz, for striking money with the letters round the edge. X is a very strong piece of iron, which has a circular opening through the centre; into this, six segments two are fitted, and between them they leave an opening W, the size of the piece of money; the interior edges of these segments are engraved with the pattern or device which it is required to impress upon the edge of the piece. The segments are fitted in the piece X by centre pins y, fig. 12., upon one of which pins each segment can rise in the manner of a centre.

The intention of this is to have a piece of money placed on the die within the space W; then, when the pressure is made upon the piece, the die descends some space, and by this motion the segments close together around the edge piece, and imprint upon the edge of it. When all the segments come into one plane, the die arrives at a firm seat, and the metal receives the stroke which make the impression on its surfaces. The die is suspended in a sort of cup, which rises and falls with the screw, nearly the same as the collar F in fig. 1.

The coining room is under the superintendence of the surveyor of the money presses, whose duties we have already described. The money, when struck, is inspected under his directions, and passed through tubes of diameter, of the different species, which readily detects any pieces which may have been im-

properly struck. The moneyers cannot coin, but in his presence, as he has every press under lock and key.

The money when examined is weighed up in journey weights for delivery to the importers of the bullion. The gold in 15 lbs.; the silver in 60 lbs. Troy.

Before this money, however, is delivered to the importers, it is carried to the mint office, to undergo inspection, and to be pixed. The inspector examines the coin as to its workmanship, and may reject it if faulty. The process of pixing is more important, as by it the perfection of the money, as to weight and fineness, is determined before it is delivered to the importers. The process of pixing, as it is called, consists in taking from every journey weight of gold and silver, a pound in tale promiscuously, by the weigher and teller. This is weighed in a very accurate balance by the King's assayer master, who declares aloud the minus or plus upon each lb., and which is recorded by the comptroller, King's clerk, and King's assay master. This determines whether the company of moneyers have made the money within the remedy allowed upon the pound Troy. As the remedy, however, upon the pound Troy is divided among the number of pieces in it, the same pound weighed is handed to the comptroller, who, in a delicate balance, weighs several pieces individually; and, if they exceeded the remedy, he could, in conjunction with the other check officers, order the coin to be remelted and recoined at the expence of the moneyers. From the same pound weight of silver or gold, the comptroller takes two pieces; the one for the King's assayer master to assay, in order to prove that the company of moneyers have in no way or degree deteriorated the quality of silver or gold in any of their processes, or from the time of its having come into their possession. The other piece is ensealed in a packet, and put into a box (called the pix-box), which is locked up under the separate keys of the said officers, there to remain until the final trial of the pix by jury, before the King, or such of his Council as are usually appointed at Westminster or elsewhere, for that purpose. When the King's assay master has proved the piece delivered to him to be of the right standard (and which, in this case, is taken as the average of the whole journey weight), he authorizes the money to be delivered to the importers of the bullion. During the period, however, in which the assay is making, the money is deposited in the strong-room of the mint treasury, under the separate keys of the master, comptroller, and company of moneyers. The money is delivered over to the importers by the weigher and teller, and in the presence of the master, comptroller, King's clerk, and one of the moneyers; the master receiving a receipt for the same, as described in the duties of the deputy-master and workers.

As the trial of the pix at Westminster is very ancient and curious, and though done in an open court, is yet so little known, it may not be uninteresting to trace it from the earliest period in which it is to be found in our records,—to state the changes which it has undergone, and the manner in which it is conducted in the present times.

The Rev. R. Ridding, to whom we acknowledge

ourselves much indebted for much valuable information in the preceding pages, gives the following account of the trial of the pix.

"It does not appear that the ancients had any such public trial; and the earliest notice of the pix, which I have met with in any modern foreign mint, is in the reign of Philip VI. of France, in the fourteenth century; but whether the passage in which it occurs relates to a public trial, cannot be determined.

"The invention of it in this kingdom, or at least its introduction into our courts, is probably of high antiquity, for in the 9th or 10th of Edward I. it is mentioned as a mode well known, and of common usage. In one of those years the King, by his writ, commanded the Barons of the Exchequer to take with them Gregory de Rokesle (then master of the mint), and straightway, before they retired from the exchequer, to open the boxes of the assay of London and Canterbury, and to make the assay, in such manner as the King's Council were wont to do, and to take an account thereof, so that they might be able to certify the King touching the same, whenever he should please.

"From this record, which is the most ancient hitherto discovered relating to this trial, it appears that, previous to the above date, it had usually been made before the King's Council, but that, by the authority of the writ above quoted, it was then to be held in the Court of Exchequer, in the presence of the Barons. It was afterwards taken from their cognizance, and came again under the power of the Lords of the Council in the Star Chamber, where it is found to have been in the year 1595 (as appears from a verdict of that date), and where it continued until 1699, when it again became subject to the Court of Exchequer; under which it has remained to the present time.

"From memoranda of assays, which are still preserved in that court, it seems that this trial used to be annually; and the same is stated to have been the regular practice until the usurpation, when it was held at such times as the state pleased. At present, I believe it is not customary for the master to require it to be held until, upon his removal from the office, it becomes necessary, in order that he may receive his quietus.

"As the authority under which these trials are held occasionally varied, so did likewise the persons who sat as judges in the court. Thus, as we have seen above, they were first the members of the King's Council, then the Barons of the Exchequer, and again the members of the Privy Council, as judges of the Star Chamber, where sometimes the King himself presided; as did James I. at an assay, which was made upon the 9th May 1611.

"In 1648, a committee of Lords and Commons was appointed by order of Parliament, for the purpose of making this trial.

"At one period (in 1649), the court was held before the Lord President of the Council of State, the Commissioners of the Great Seal, and others of the Council of State, and Committee of Revenue, by virtue of an act of Parliament: at another (in 1657) by the Lords Commissioners of the Great Seal, assisted by the Lords Commissioners of the Treasury, the Justices of the several Benches, and Barons of the Exchequer, or some of them, under the authority of a warrant signed by the Protector Cromwell; and it is now com-

posed of such members of the Privy Council, as are expressly summoned for that purpose; the Lord High Chancellor, or, in his absence, the Chancellor of the Exchequer, presiding.

"The manner in which this trial was formerly conducted in the Court of Exchequer appears, from a verdict of the 11th year of Henry VI. to have been by an assay, made in the presence of the court, and of other persons who were appointed to assist, by the King's assay master, and to have been determined without the intervention of a jury.

"The earliest notice which has occurred, in which the judgment of professional artists was required to sanction, as a jury, the judgment of the court, is dated in the 37th of Elizabeth; when a trial was held in the Star Chamber.

"The number of the jurors has occasionally varied considerably. No less than nineteen names appear to the verdict of the 37th of Elizabeth; and in 1651 the moneyers speak of a jury of twenty-four men, whilst the number usual at the present time is no more than twelve.

"As I have not been able to discover any ancient ceremonial, by which the forms of this trial were regulated; I must now proceed to state the modern practice of summoning the court, and conducting the business of it.

"Upon a memorial, being presented by the Master of the Mint, praying for a trial of the pix, the Chancellor of the Exchequer moves his Majesty, in Council, to that purpose. A summons is then issued to certain members of the Privy Council, to meet at the house, which is now allotted to the office of Receiver of the Fees in his Majesty's Exchequer, at eleven o'clock in the forenoon, on a certain day. A precept is likewise directed, by the Lord High Chancellor, to the Wardens of the Goldsmiths' Company, requiring them to nominate, and set down, the names of a competent number of sufficient and able freemen of their company, skilful to judge of, and to present the defects of the coins, if any should be found, to be of the jury, to attend at the same time and place. This number is usually twenty-five, of which the assay master of the company is always one.

"When the court is formed, the clerk of the Goldsmiths' Company returns the precept, together with the list of names; the jury is called over, and twelve persons are sworn. The president then gives his charge, which was formerly to be general, like the oath, to examine by fire, by water, by touch, or by weight, or by all, or by some of them, in the most just manner, whether the monies were made according to the indenture, and standard trial pieces, and within the remedies. But, in 1754, the Lord High Chancellor Talbot directed the jury to express precisely how much the money was within the remedies, and the practice which he thus enjoined is still continued. The other parts of the charge necessarily vary, according to the ability of the president, and his knowledge of the subject.

"When it is concluded, the pix is delivered to the jury, and the court is commonly adjourned to the house of the president, where the verdict is afterwards delivered.

"The jury then retire to the court-room of the duchy

Machine for casting the Ingots of Silver, at the Mint.

Fig. 5.

Laminating Rollers. Fig. 6.

Fig. 7.

COINING.

Machines used in the Mint.

PLATE LXII.

Fig. 4.

Fig. 1.

Fig. 2.

Fig. 3.

M^r Barton's Machine for reducing Plates of Metal to an equal thickness.

Fig. 6.

Fig. 9.

Fig. 7.

Fig. 8.

Perspective View.

Fig. 5.

Published by A. Constable & Co. Edin^g 1818.

COINING.

MACHINES used in the MINT.

PLATE LXIII.

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Fig. 5.

Fig. 6.

Fig. 7.

Fig. 8.

Circular Shears.

Fig. 8.

COINING.

PLATE LXIV.

COINING PRESS used in the ROYAL MINT.

The image is a technical plate titled 'COINING. PLATE LXIV.' It illustrates a 'COINING PRESS used in the ROYAL MINT.' The central figure, labeled 'Elevation.' and 'Fig. 1.', is a large, detailed drawing of the machine's main body. It features a central vertical shaft (A) with a large gear (B) and various adjustment mechanisms (C, D, E, F, G, H, I, K, L, M, N, O, P, Q, R, S, T, V, W, X, Y, Z). Surrounding this central figure are 19 smaller diagrams, each labeled with a figure number and a letter: Fig. 2 (F, V, W), Fig. 3 (F, S, P, Q), Fig. 4 (L), Fig. 5 (G, W, G, g), Fig. 6 (T, t), Fig. 7 (A, m), Fig. 8 (O, L, M), Fig. 9 (O, N, M, P, L, P), Fig. 10 (P, P, L), Fig. 11 (X, T, V, X, t), Fig. 12 (W, X, X), Fig. 13 (W, W, W, W, W, W, W, X, X), and Fig. 14 (L, t). These smaller diagrams show individual components like the die (F), the press foot (T), the gear (A), and the adjustment levers (P, Q, R, S, T, V, W, X, Y, Z).

of Lancaster, whether the pix is removed, together with the weights of the exchequer and mint, and where the scales which are used upon this occasion are suspended, the beam of which is so delicate, that it will turn with six grains, when loaded with the whole of those weights, to the amount of 48 lb. 8 oz. in each scale.

"The jury being seated, the indenture, or the warrant under which the master has acted, is read. Then the pix is opened, and the money which had been taken out of each delivery, and enclosed in a paper parcel, under the seals of the warden, master, and comptroller of the mint, is given into the hands of the foreman, who reads aloud the indorsement, and compares it with the account which lies before him. He then delivers the parcel to one of the jury, who opens it, and examines whether the contents agree with the indorsement.

"When all the parcels have been opened, and found to be right, the monies contained in them are mixed together in wooden bowls, and afterwards weighed.

"Out of the said monies so mingled, the jury take a certain number of each species of coin, to the amount of one pound weight, for the assay by fire; and the indented trial pieces of gold and silver, of the dates specified in the indenture, being produced by the proper officer, a sufficient quantity is cut from either of them, for the purpose of comparing with it the pound weight of gold or silver which is to be tried (after it has been previously melted and prepared) by the usual methods of assay.

"When that operation is finished, the jury return their verdict, wherein they state the manner in which the coins they have examined have been found to vary from the weight and fineness required by the indenture, and whether, and how much, the variations exceed, or fall short of, the remedies which are allowed; and, according to the terms of the verdict, the master's quietus is either granted or withheld."—Archæologia, Vol. XVI.

We shall conclude our observations upon the subject of coinage, by detailing the mode of manufacturing the dies. An original die is engraved upon a piece of soft cast steel, of the size of the money to be made. The table of the die must be perfectly level or square. The impression engraved is, of course, cut into the steel, and its depth in proportion to the relief ultimately wanted upon the coin. When the engrav-

ing is finished, the die, or matrix, as it is called, is hardened. This is a very nice process, and requires considerable care to perform it. The die is put into a cast iron pot, completely embedded in animal charcoal, chiefly made from leather. The pot is placed in an air furnace in which coke is burned, which gives a more steady and uniform degree of heat. The square of the furnace is also considerably larger than the pot, that the die may have the greatest possible equality of temperature. When the die has attained its proper degree of heat, it is withdrawn from the furnace, and immersed in a large cistern of water, the temperature of which is kept as uniform as possible by a stream of cold water constantly flowing in and out of the cistern, while the process of hardening continues. It frequently happens, that in this process (either from the steel being faulty or heated to excess) the die will fly in pieces, and the whole labour of the artist is lost. When, however, the matrix is perfect, it is placed in the multiplying die press, which works in every respect like a coining press, but moved by men. An impression is taken from the matrix upon a blank die of cast steel, similar to the mode of impressing the money. The blank die is fixed as the lower die of the coining press; and, by working the screw of the press, which has very long and heavily loaded arms, the matrix is made to strike the blank die with great force, and bring its impression in relief upon its surface. The hardness, by compression of the steel, is so great, that an impression of the matrix cannot be obtained without annealing the die perhaps twice or three times, which is done in iron pots, as in the case of hardening, but are allowed to cool gradually. An impression taken in this way is called a puncheon die. When the engraver has given all the delicate outlines of the original to it, it is hardened in the same manner as its original, and used to give impressions to blank dies by a similar process, the impression being sunk into the dies, which dies being used for coinage, gives the impression in relief to the money.

This important department of the mint is under the superintendence of the clerk of the irons, who never suffers the multiplying press to be used but in his presence. He has also the care of all the dies, and must account to the Board of Management for all matrixes, puncheons, and dies, made and destroyed in the mint.

(A. A.)

C O L D.

It is often disputed whether Cold has any actual existence, or should be considered as merely the privation of Heat. Nor is that question of a modern date; Plutarch attempted to discuss it, in his Tract De primo frigido, and the reasonings which he there employs, though abundantly vague, are yet curious. Cold, he says, affects the senses as well as heat; and it is not less active, since it condenses and consolidates bodies. He, therefore, inclines to the opinion, that cold is a distinct and independent power in nature. With the Stoic philosophers, he regards air as by its constitution cold and dark; and hence water drawn from a well freezes on being exposed to the atmosphere, while rivers over-

shadowed by high banks seldom freeze, and even where their surface congeals, the heat is not exhaled, but only driven down nearer the bottom.

It is contrary to sound physics to admit more principles than are indispensably required, and this argument alone may be sufficient for the rejection of cold as a distinct power in nature. What we term cold, in reference to our feelings, is merely the diminution of heat. But the existence and materiality of heat rest on a very different foundation. The introduction of heat into a body is accompanied by the infusion of a certain extrinsic repulsive force, and its passage through the mass is connected with a series of depending internal motions, which imply the regular expenditure of time and ve-

locity. The contraction which follows on the diminution of heat, is due to the mutual attractive powers of the particles of the substratum, now exerted with less opposition. That expansion, again, which some fluids manifest in the act of congelation, proceeds from the operation of the principle of crystallization, with the recondite nature of which we are still unacquainted.

The notion that cold has a separate and independent existence appears, however, to receive some countenance, from the elegant experiment of collecting and concentrating the frigorific impressions in the focus of a metallic reflector. This curious fact is one of the oldest in physical science, but again lately revived, and combined with circumstances of peculiar interest. The experiment was first mentioned about the year 1590, by Baptista Porta, in the enlarged edition of his Magia Naturalis, when the four books of which it originally consisted were augmented to twenty, at the very time that his ingenious countryman, Sanctorio, had invented and applied to medical purposes the air-thermometer. Porta relates, that, if a shut eye be held in the focus of a speculum before which is placed a ball of snow, intense cold will be felt on the eye-lid.* Cavalieri, the celebrated discoverer of infinitesimals, in his work on the conic sections, printed in 1632, and entitled Lo Specchio Ustorio, extended the experiment to all impressions which he conceived to be propagated in straight lines—not only to those of heat and cold,—but to those of sound and even smell.† It was afterwards frequently repeated at Florence, by the Academy del Cimento, with the important addition of the thermometer, which that learned body had the merit of introducing into practice. Similar experiments were next performed by Mariotte in France. Specula and burning glasses appear, in the sequel,

to have been allowed to fall into great neglect. We find scarcely any mention of their application to physical researches, till after the lapse of more than half a century, Kraft repeated, at St Petersburg, during the severe winter of 1740, the frigorific experiment of the Italian philosophers, with a reflector belonging to the Cabinet of the Imperial Academy. Ambitious to operate on a grand scale, he selected three huge blocks of clear ice, nearly of a cubical form, each side being 2, 4, and 5 feet; but to save the trouble of transporting them, he carried the speculum out of doors. No sensible effect, however, was then perceived by him, though he used the air thermometer on account of its extreme delicacy. In 1744, this Academician again resumed the observation, and with scarcely better success, having obtained only a doubtful cold of three degrees. The cause of the failure was evidently, his performing the experiment out of doors, and not in a warm room. The blocks of ice had, by long standing, acquired almost the same temperature as their ambient medium. Had the air happened to become suddenly colder, they might, from their relative condition, have excited impressions even of heat, and thus have perplexed philosophy for many years afterwards.

Such unsatisfactory results, from the action of a mass of ice of above a ton weight, seem, for a long time, to have shaken the belief in former experiments; and the subject was almost forgotten, when Pictet of Geneva, in 1781, repeated the original observation on a small scale, indeed, but with entire success. Since that time, a pair of brass reflectors, with a wire case for holding charcoal or snow, has been deemed an essential apparatus in every physical cabinet. The concentration of cold in the focus of a speculum, always excites surprise; and the experiment is often exhibited with a sort of mysterious air, as if

* Si quis candelam in loco, ubi spectabilis res locari debet, apposerit, accedet candela per aërem usque ad oculos, ut illos calore, et lumine effendet; hoc autem mirabilis erit, ut calor, ita frigus reflectitur, si eo loco nix obiciatur, si oculus retigerit, quia sensibilis, etiam frigus percipiet.

† Cavalieri mentions that, with a spherical speculum made of lead and indifferently polished, he was able to inflame dry substances by the reflexion of a charcoal fire; and that, with a deep truncated parabolic speculum badly polished, he produced the same effect in the open focus, from a small fire of wood at the distance of five feet.—Esperienza di questo hò fatto io, che con vno Specchio sferico di piombo ancor mal polito, hò acceso il fuoco nella materia arida al fuoco di carboni; e di più l'hò fatto con la superficie parabolica, cioè con vn canone parabolico, che hauea il suo foco vicino alla cima, essendo esso specchio parabolico troncato pur nella cima, qual' era di stagno, e mal polito, tal che opponendolo al fuoco, ò alla fiamma di ben poca legna, nella distanza di tre braccia, ponendo la mano lì, dou era la parte troncato, et il foco della parabola, non vi si potea sostenere, anzi vi s'accese fuoco; la qual cosa potria alcuno applicare al riscaldaméto delle stanze, ò alle distillazioni, pp. 85. 86.—In general, says this ingenious mathematician and philosopher, the same form of speculum which concentrates light and heat, must likewise collect cold, which spreads from its source, from a mass of snow, for instance, in straight lines. The hyperbola is, therefore, the figure which he thinks the best adapted for the purpose; and he proposes this for condensing the smells radiated from an odoriferous substance.—Hòra dunque basterà quello, che si è detto di sopra intorno al lume, e calore, potendo noi nell'istesso tempo intendere le medesime cose anco per il freddo, che dilatandosi dal corpo freddo ad ogni posizione per linea retta, e perciò nell' infinite linee, che si partono dal corpo freddo, come dalla neve, essendoui dentro le parallele, che sono vnite dallo specchio parabolico, e le diuergenti, che sono vnite dall' elittico, e le conuergenti vnite dall' iperbolico, con opporre alcun di questi specchi ad vna massa di neve, ò di ghiaccio, sentiremo nel loro foco essere il freddo fatto molto gagliardo, ma per questo effetto sarà più atto l'iperbolico di tutti, come quello, che raccoglierà maggior quantità di linee fredde; e questo basti ancora circa il freddo, potendosi forse in vn certo modo creder, che tale effetto accadesse anco intorno à gli odori, provando noi dilatarsi pur quelli dalli corpi odoriferi verso ogni banda. Id. p. 128.

Cold. it established, or at least rendered probable, the distinct and material existence of cold. But, in fact, it is not more difficult to conceive the impressions of cold to be collected than those of heat. Both those impressions are only relative to the temperature of the atmosphere, which serves as the medium of their transmission. The one process terminates with the deposition of a portion of heat, the other with its abstraction.

Sources of Cold. The diminution of heat, or the increase of cold, is produced in Nature under four different circumstances: 1. By the obliquity or absence of the sun; 2. By the tenuity of the higher atmosphere; 3. By the evaporation which takes place in dry air; and, 4. By the chilling impression shot downwards from a clear and serene sky.

Obliquity of the Sun. 1. In our temperate climates, the thermometer in winter very seldom descends 15 degrees on Fahrenheit's scale, below the point of congelation. But, in the higher latitudes, the intensity of the cold is often far greater. In the northern parts of Sweden and Russia, the rivers and ordinary lakes are frozen to the depth of several feet; wine, and even ardent spirits, become converted into a spongy mass of ice, and, as the cold still augments, it penetrates the living forests, and congeals the very sap of the trees, which occasionally burst from this internal expansion with tremendous noise. The Baltic Sea has been repeatedly covered with a solid floor of ice, capable of transporting whole armies, with all their stores and engines of war. Those waters, indeed, are only brackish; but the more northern ocean itself has often been frozen to a very considerable thickness. In Siberia and Hudson's Bay, and even in the northern provinces of Sweden, mercury has been at some times observed contracted by exposure into a solid semi-metal; and, consequently, the cold which then prevailed must have exceeded 71 degrees, or 39 below the commencement of Fahrenheit's scale.

Elevation of the Place. 2. In elevated tracts the increase of cold is very striking. Even at an altitude of three miles and a half, the air is generally 68 degrees colder than at the level of the sea. On the summit of the Andes, therefore, a thermometer would often sink perhaps under the beginning of Fahrenheit's scale; and it seems probable that mercury would naturally freeze in winter on the top of Mont Blanc. Mountains are hence regarded as the grand stores or depositories of cold in the milder climates. In every country, therefore, the air of subterranean caves, and the water of deep springs or wells, are during the summer months comparatively cold. Hence the obvious advantage of cellars, in addition to their preserving an uniform temperature, which is so favourable to the ripening of the liquors deposited in them. But the air at the bottom of an open and very deep pit must be colder than the mean state of the ground, for in all the changes which take place at the surface, the cold air will descend, and the warm air still float over the mouth of the pit. The wealthy classes of antiquity were accustomed, accordingly, to cool the wine for their tables, by suspending it for some time in a bucket let down near the surface of profound wells.

3. Evaporation is a natural process, by which heat is powerfully abstracted by the exhaling moisture, while this assumes a gaseous constitution in the act of combining with dry air. The fact seems to have been known in the warm regions of the east at a very early period of society, suggested probably by the familiar use of a rude unglazed pottery for all culinary purposes. The Egyptians, and other inhabitants of the sultry shores of the Levant, have, from the remotest ages, cooled the water for drinking in their porous jars. Athenæus reports, from a history of Protagorides, that King Antiochus had always a provision for his table prepared in that way. The water having been carefully decanted from its sediment into earthen pitchers (ὄδοντες πρᾶκται), these were transported to the highest part of his palace, and exposed to the clear and keen atmosphere (ἡλιακὸν ἄνδρον), two boys being appointed to watch them the whole night, and keep constantly wetting their sides. This labour of sprinkling the surface of the jars seems to have been afterwards spared, in consequence probably of the adoption of a more porous kind of earthen-ware. Galen, in his Commentary on Hippocrates, relates, that he witnessed the mode of cooling water, which was practised in his time, not only at Alexandria, but over all Egypt. The water, having been previously boiled, was poured at sun-set into shallow pans (ἀγγίαι ἑξακίνοι), which were then carried to the house-tops, and there exposed during the whole night to the wind; and to preserve the cold thus acquired, the pans were removed at day-break, and placed on the shaded ground, surrounded by leaves of trees, prunings of vines, lettuce, or other slow conducting substances.

The bottles or bags made of goat-skins, in which the wandering Arabs are wont to carry their scanty provision of water, allowing a small portion of the liquid to transude and exhale, render it by consequence comparatively cool, and better fitted to mitigate or allay the intolerable thirst created in traversing their sandy deserts. In Guinea, it is customary to fill gourds or calabashes with water, and suspend them all night from the outer branches of trees.

The Moors introduced into Spain a sort of unglazed earthen jugs, named bucaros or alcarrazas, which, being filled with water, present to the atmosphere a surface constantly humid, and furnish by evaporation, during the dry and hot weather, a refreshing beverage. The same practice has been adopted by degrees in various parts of the south of Europe. In India, during certain months, the apartments are kept comparatively cool, by dashing water against the matting of reeds or bamboos, which line the doors and the outside of the walls. Even the more luxurious mariners, in their voyages between the tropics, are accustomed to cool their wines, by lapping the bottle with wet flannel, and suspending it from the yard or under the cabin-windows. In all such cases, the effect is accelerated, though not augmented, by the swiftness of the current of air. What have been called Egyptian coolers, and lately produced by our potters, are less perfect in their operation. Being very thick, they require only to be soaked in water, and the evaporation from their

surface cools the adjacent air. On the inside, however, where the bottle is placed, the action, in consequence of the confined humidity, must be enfeebled. In damp weather, those vessels, it is evident, are entirely useless.

The natives of India likewise are enabled, by directing a skilful process of evaporation, to procure for themselves a supply of ice during their short winter. In the upper country, not far however from Calcutta, a large open plain being selected, three or four excavations are made in it about thirty feet square and two feet deep, and the bottom covered to the thickness of nearly a foot with sugar canes or dried stalks of Indian corn. On this bed are placed rows of small unglazed earthen pans, about an inch and quarter deep, and extremely porous. In the dusk of the evening, during the months of December, January, and February, these are filled with soft water previously boiled and suffered to cool, when the weather is very fine and clear a great part of the water becomes frozen during the night. The pans are regularly visited at sunrise, and their contents thrown into baskets which retain the ice. These are now carried to a conservatory made by sinking a pit 14 or 15 feet deep, lined with straw under a layer of coarse blanketing. The small sheets of ice are thrown down into the cavity, and rammed into a solid mass. The mouth of the pit is then closed up with straw and blankets, and sheltered by a thatched roof.

4. It was stated in the article CLIMATE, that impressions of cold are constantly showered down from a clear and azure sky. These effects are no doubt more conspicuous in the finer regions of the globe. Accordingly, they did not escape the observation of the ancients, but gave rise to opinions which were embodied in the language of poetry. The term Αἴε was applied only to the grosser part of the atmosphere, while the highest portion of it, free from clouds and vapour, and bordering on the pure fields of æther, received the kindred appellation of Αἰθέρ. But this word and its derivatives have always been associated with ideas of cold. We have seen that the verb Ἰαῖθραζω is used by Athenæus to signify, the cooling of a body, by exposure under a serene sky. Homer uses the term Αἰθέρ, in speaking of the reception of his hero, when overcome with cold and toil.* The same poet of nature applies the epithet Αἰθηνής or Αἰθηνίης or frigorific, to Bo-reas, the north wind.† The chorus in the Antigone of Sophocles deprecates the pelting storm, and likewise the cold (αἰθέρ) of inhospitable frozen tracts.‡ The word αἰθέρ is employed by Herodotus to signify a chill as well as a dry atmosphere.¶ Of the same import is the expression in Horace—Sub Jove frigido.

In the finer climates, especially, a transpiercing cold is, therefore, felt at night under the clear and sparkling canopy of heaven. The natives carefully avoid exposing themselves to this supposed celestial influence; yet a thin shed of palm leaves may be mats. sufficient at once to screen them from the scorching rays of the sun, and to shelter them against the chilling impressions rained from the higher atmosphere. The captains of the French gallees in the Mediterranean used formerly to cool their wines in summer, by hanging the flasks all night from the masts. At day-break, they were taken down and lapped in several folds of flannel, to preserve them in the same state. The frigorific impression of a serene and azure sky, must undoubtedly have concurred with the power of evaporation, in augmenting the energy of the process of nocturnal cooling, practised anciently in Egypt, and now systematically pursued in the higher grounds of India. As the chillness accumulated on the ground is greatest in clear nights, when the moon shines brightest, it seemed very natural to impute this effect partly to some influence emanating from that feeble luminary. It was long imagined that the lunar beams are essentially cold; and some philosophers, at no remote period, have attempted even to prove the fact by experiment. Mr Boyle, though he rejected judicial astrology, was yet disposed to admit the notion of stellar influences.

The obvious mode of cooling water, or other liquids, by the infusion of ice or snow, was practised in the warmer countries from the earliest ages. It is even mentioned in the Proverbs of Solomon: "As the cold of snow in the time of harvest, so is a faithful messenger to them that send him." Aristotle, presuming that the finer parts of water are dissipated by congelation, maintained that it is pernicious to drink melted snow. This speculative opinion seems not, however, to have been regarded by the ancients. Theocritus calls snow-water an ambrosial drink,—πᾶς αἰθέρ. Xenophon mentions the practice of cooling wine, by the addition of snow. It is related by the historians of Alexander the Great, that, in his Indian expedition, when he laid siege to the city of Petra, he commanded thirty pits to be dug and filled with snow, which was covered over with oak branches. The luxurious Romans had excavations regularly formed for keeping snow the whole year, chaff and other light substances being employed to preclude from it the access of heat. But, as the snow, preserved in this way, could not escape being soiled, instead of mixing it directly in the drinking cup, a more refined practice was introduced, of surrounding the silver goblet which contained the liquor with a mass of the melting snow. This improvement was ascribed to the profligate emperor Nero. Similar modes of storing up

* Αἴεθρ και καμάτην διδμημύνει ἦν ἰς ἄνω.
Odys. Lib. XIV. 318.

† Ὅς δ' ἔτι ταρταρίῃ πρᾶσιν Διὸς ἰκονομίαν,
ὑπὸ γαῖαν ὑπὸ τὸν αἰθηνήν ὕψος.
Ilad. Lib. XIX. 357-8.

Καὶ βήνις αἰθηνήνις, μέγα κῆμα κλύσιν. Odys. Lib. V. 296.

‡ δυσαιθήνις πάγην ἄνδρα
καὶ δυσαιθήνις φάγην βίην. Antigone, 357.

¶ Θειμήτην γὰρ δὴ ἐπὶ τὸ ὕδωρ τῆς αἰθέρης καὶ τῆς ὕδωρ.
Eulerpe.

Cold. snow have been adopted in all the warm countries. The caves on the sides of Mount Ætna are considered as natural magazines, for supplying a material which is not only carried down to Palermo and Messina, but even shipped to the island of Malta. The Italians formerly cooled their wine, by setting the large glass flasks containing it, in wide vessels of wood or cork, the intervening space being filled with snow, on which water was poured.

cooling with nitre. Saltpetre or nitre being almost a natural production of the east, its property of rendering water cold by solution, was probably known, from a very remote period, to the oriental nations. This process of cooling is described in the Institutes of Akbar as the discovery of that enlightened prince, who governed India with parental mildness, from the year 1560 to 1605. One part of nitre is directed to be thrown into a vessel containing two parts of water, and a gugglet of pewter or silver filled with pure water, and having its mouth close stopped, is then stirred quickly in the mixture for the space of a quarter of an hour.

introduced to Italy. The frigorific property of nitre was probably first communicated from India or Persia to Europe, and seems to have become known to the Italians about the middle of the sixteenth century. As early as the year 1550, all the rich families in Rome cooled the liquors for their tables, by dissolving that salt in water. Into a vessel of cold water, the nitre was gradually added in the proportion of a fourth or fifth part, while a globular bottle, with a long neck, containing the wine or water to be cooled, was whirled rapidly round its axis. The salt, being afterwards recovered by crystallization, would always serve the same purpose again, with undiminished effect. In India, every family of distinction keeps a domestic, whose sole employment is to cool liquors by this process; but nitre being cheap in that country, it is used in larger proportions, and the water charged with it is allowed to become a perquisite of the operator.

cooling by Lime Powder. The application of salts to produce cold was extended by Boyle, and afterwards more successively by Fahrenheit. But, within these twenty years, Mr Walker of Oxford, and Professor Lowitz of St Petersburg, have resumed the subject, and produced compound saline powders, possessed of intense frigorific power. The solution of salts in water, expanding that liquid, augments its capacity for heat, and consequently depresses its temperature. This effect is likewise the greater, in proportion to the quantity of saline matter which can be dissolved. But after water is saturated with one species of salt, it can still absorb some portion of another. Hence the frigorific effects of solution are always increased, by employing a compound dry powder. Nitre and sal-ammoniac, or the nitrate of potash and the muriate of soda in equal parts, added in the form of a dry powder to three parts by weight of water, will sink Fahrenheit's thermometer 40 degrees. But equal parts of the muriate of ammonia and of the nitrate of potash, with one part and a half of the sulphate of soda or common Glauber's salt, will cool down three parts of water 46 degrees. A still greater effect, amounting

to 57 degrees, is produced, by dissolving equal parts of the nitrate of ammonia and of the carbonate of soda, in one part of water. The frigorific action is in general augmented, by throwing the desiccated powder into dilute acid instead of water. Thus, three parts of the phosphate of soda and two parts of the nitrate of ammonia joined to rather more than one part of weak nitric acid, will sink the thermometer 71 degrees.

Principle of Evaporation. These changes induced on the temperature of the liquid menstruum are, no doubt, considerable, yet they are still only transient, and the process requires some address and manipulation, not always readily attained. But the principle of evaporation, when rightly understood, leads to a far easier mode of cooling liquids, which may be prolonged at pleasure. A close investigation of that principle, at the very commencement of his philosophical labours, has conducted Professor Leslie through the whole train of his discoveries on the subject of refrigeration. The process of evaporation had not then been examined with attention. The depression of temperature which always accompanies it, was hastily supposed to be proportional to the rate with which the moisture is dissipated, and to be therefore augmented by every circumstance that can accelerate this effect. If water, contained in a porous vessel, expose on all sides its surface to a current of air, it will cool down to a certain point, and there its temperature will remain stationary. The rapidity of the current must, no doubt, hasten the period of equilibrium, but the degree of cold thus induced will be still the same. A little reflection may discover how this happens. Though the humid surface has ceased to grow colder, the dispersion of invisible vapour, and the corresponding abstraction of heat, still continues without intermission. The same medium, therefore, which transports the vapour, must also furnish the portion of heat required for its incessant formation. In fact, after the water has been once cooled down, each portion of the ambient air which comes to touch the evaporating surface must, from its contact with a substance so greatly denser than itself, be likewise cooled to the same standard, and must hence communicate to the liquid its surplus share of heat, or the difference between the prior and the subsequent state of the solvent, which is proportional to the diminution of temperature it has suffered. Every shell of air which encircles in succession the humid mass, while it absorbs, along with the moisture which it dissolves, the measure of heat necessary to convert this into steam, does, at the same instant, thus deposit an equal measure of its own heat, on the chill exhaling surface. The abstraction of heat by vaporization on the one hand, and, on the other, its deposition at the surface of contact, are, therefore, opposite contemporaneous acts, which soon produce a mutual balance, and thereafter the temperature induced continues without the smallest alteration. A rapid circulation of the evaporating medium may quicken the operation of those causes; but, so long as it possesses the same drying quality, it cannot, in any degree, derange the resulting temperature. The

heat deposited by the air on the humid surface becomes thus an accurate measure of the heat spent in vaporizing the portion of moisture required for the saturation of that solvent at its lowered temperature. The dryness of the air is therefore, under all circumstances, precisely indicated, by the depression of temperature produced on a humid surface which has been exposed freely to its action.

Guided by these views, Mr Leslie was enabled to construct a correct Hygrometer that should indicate the dryness of the air, from the diminution of temperature which a small body of water, exposed on all sides, suffers by evaporation. His efforts again to improve this instrument, led him next to the invention of the Differential Thermometer, which was converted into an hygrometer, by having one of its balls covered with cambric, lint or tissue paper, capable of being easily wetted. Reduced to such a delicate and commodious form, it detected, with the utmost precision, and under all circumstances, the relative condition of the air in regard to dryness.

It appears that absorbent substances, exposing a broad surface, are capable of assimilating to their previous state the air confined over them. Flannel, for instance, which has been intensely dried, will support a remarkable degree of dryness in a close receiver. The trap-rock and compound clays, brayed into a coarse powder, and desiccated before a strong fire, will exert a more powerful and extended action. But dried oat-meal will act with equal energy, and for a longer time. Of the saline substances, the muriate of lime absorbs moisture with the greatest and most protracted force. After it has become drenched with humidity, it may likewise be recovered again, though the process of restoring it unaltered is rather troublesome. But the best and most powerful absorbent is the concentrated sulphuric acid, or the oil of vitriol of commerce, which continues for a long time to attract moisture with almost undiminished force, and possesses, besides, the valuable property, after it has become charged with humidity, of being easily restored again, by the application of heat, to its original strength.

To cool water, in any climate or state of the atmosphere, we have only therefore to put it into a small porous vessel, presenting on all sides a humid surface, and to suspend this within a close wide cistern, of which the bottom is covered with a layer of sulphuric acid. The broad surface of the acid, absorbing the moisture as fast as it diffuses itself through the confined air, keeps that medium constantly at a point of extreme dryness, and thus enables it to support, with undiminished vigour, the process of evaporation.

In practice, the cistern or refrigeratory, having a broad cylindrical form, from twelve to sixteen inches in diameter, and composed of dense well-glazed earthenware (See Plate LXV. fig. 7.), is placed in a cellar or other cool place, and charged with sulphuric acid to the height of about half an inch from the bottom. One of the porous earthen pots, being filled up to the lip with water fresh drawn from the well, is set upon a low porcelain stand in the middle of the cistern, to which the lid or cover is then care-

fully adapted. In the space of from three to perhaps five hours, the cooling is nearly completed, and the pot should now be removed: for though the water will be kept at the same degree of coldness as long as it remains shut up within the refrigeratory, the acid would be unnecessarily weakened by the incessant absorption of moisture.

The production of cold is greater when the cistern is large, or when a small pot is used, inasmuch that the effect will be diminished one half, if the humid surface should equal that of the acid, the opposite actions of such surfaces inducing an exactly intermediate state, with respect to dryness and moisture, in the condition of the aerial medium. The power of evaporation is also diminished in the low temperatures. Thus, if the atmosphere were at 95°, by Fahrenheit, the water within the refrigeratory might be cooled down 30°, or brought to 59°; but if the thermometer be at 50° the water can be cooled only 18°, which brings it to the freezing point. This seems to be a very convenient property, since the power of the refrigeratory is always the greatest at the season when its application is most wanted.

It is easy, therefore, by such means, to cool water in our climate at all times, to near the freezing point, and, even under the torrid zone, to reduce it to the temperature of 60 degrees, which, in those regions, is sufficient perhaps for essential comfort.

By supplying a succession of porous earthen pots, the acid will continue to act with scarcely diminished force, till it has absorbed half its weight of moisture: during which time it will have assisted in cooling about fifty times that quantity of the water exposed to evaporation. At this stage, the dilute acid should be drawn off, and a charge of concentrated acid again introduced into the refrigeratory.

This method of procuring cold, it will readily be perceived, could be employed with advantage for various domestic purposes. For instance, butter may in summer be kept cool for the table, by putting it, after being washed with water, into a wet porous pot, and shutting this up for a couple of hours in the refrigeratory. To cool wine sufficiently, one bottle only is used at a time in the smallest refrigeratory: A sheath of stocking or flannel previously soaked in water being drawn over the body of the bottle, it is laid in a reclined position on one of the porcelain sliders, near the surface of the acid, and allowed to remain shut up during the space of three or four hours.

The refrigerating combination here employed produces its effect, by a sort of invisible distillation carried on by the play and circulation of the included air. The minute portions of moisture which successively combine with the contiguous medium, must abstract from the mass of water as much heat as would support them in the state of vapour, or would in ordinary cases convert them into steam. This vapour again, being conveyed through the air, is attracted by the sulphuric acid, and, recovering its liquid constitution, deposits the heat which it had borne away. The acid is therefore warmed at the expence of the water subjected to evaporation, and the whole performance of the apparatus consists in a mere transfer and interchange of condition.

Is the passage of any substance from the liquid to a solid form, in consequence of the abstraction of heat. The conversion of water into ice could not fail to draw the notice of men in all ages. The minute and divided fragments of the same production, which descend from the clouds in the shape of snow or hail, displayed the various powers of nature. The ancients imagined, that water which has lain for ages in a frozen state acquires at last a permanent consolidation. They extended, accordingly, the name of ice (ἱεῖς or crystal) to the pure and pellucid kind of quartz, which often occurs on the sides of lofty mountains, near the boundary of perpetual congelation.

It was early remarked that melted ice has the lightness and quality of boiled water. In fact, the portion of air combined with ordinary water is discharged in the act of freezing as well as in that of boiling. Water thus deprived of its air, is therefore prepared for a readier congelation. The ancients accordingly, we have seen, always boiled the water which they designed afterwards to cool. Aristotle relates in his Meteorology, that the fishermen who cast their nets in the Pontine Lake, used to carry in close vessels boiled water, for the purpose of sprinkling the reeds, that these might quickly freeze together, and cease to disturb the fish by their rustling noise. The expulsion of air from water during the progress of congelation, was afterwards fully proved by Mariotte, one of the earliest members of the French Academy of Sciences. If two wine glasses, filled, the one with water from the well, and the other with water recently boiled, be exposed to the frost, the ice of the latter will seem almost uniformly pellucid, while the ice of the former will appear charged with small air-bubbles crowding towards the centre of the mass, to which they are driven by the advance of the congelation.

That congelation shoots at angles of 120 degrees, was first observed in the beginning of the seventeenth century by the great Kepler; and this ardent and inventive genius, in an elaborate Dissertation, which he printed as a New Year's present, investigated the various forms and modifications of the icy crystals. The subject was next discussed by Des Cartes and Bartholinus, and about a century afterwards resumed by Mairan, and may be considered as a step towards the general theory of crystallography, which has been since reared by the patience and ingenuity of Håuy.

Other liquids, such as vinegar, dilute mineral acids, weak spirits, and saline solutions, are likewise capable of being frozen; but they yield an ice distinctly different from that of pure water, resembling an aggregation rather than an uniform solid, and wanting consistency, strength, and clearness. The frost appears to seize on the water only, and to fill the compound liquid with close spicular shoots, entangling the stronger acid or brine in their interstices. It was a mistake, therefore, to assert that the ice of sea-water is really fresh. In the process of melting, some portion of the brine may probably flow off, but

the residue still is always brackish. This fact is even positively stated by the missionary Crantz, in his accurate account of Greenland. The very intelligent and enterprising navigator, Mr Scoresby, reckons the specific gravity of the spongy salt-water ice to be .873, while that of fresh-water ice amounted to .937.

The ancients were altogether unacquainted with artificial congelation, and with any cold, indeed, below that of freezing. The application of nitre to the cooling of water seems, before the close of the sixteenth century, to have suggested to the Italians the experiment of mixing it with snow. A very intense degree of cold was thus generated, capable of converting speedily into solid ice a body of water contained in a smaller vessel immersed in the dissolving mixture. Sanctorio, who may be regarded as the father of modern physics, mentions, in his Commentary on Avicenna, that he produced the same effect, by employing common salt instead of nitre, in the proportion of the third part of the snow, and had repeatedly performed the experiment in the presence of a numerous auditory.

From Italy, this discovery was gradually communicated over the rest of Europe. In the course of the seventeenth century, iced creams, fruits, and various confitures, were first produced on the tables of the luxurious. The famous coffee-house, Procope, was founded at Paris in 1660, by a Florentine of that name, a vender of lemonade, who was very successful in the art of preparing rich ices. Thirty years afterwards, the use of such artificial delicacies in that city had become quite common.

The cold resulting from the addition of saline powders to snow or pounded ice, depends on the more powerful attraction of those salts which restores the frozen mass to its liquid form, and therefore augments its capacity for heat. Fahrenheit fixed the commencement of his thermometrical scale at the temperature of the compound of salt and snow, conceiving it to be the lowest possible. But much lower degrees of cold are now produced. One part of the muriate of soda, or purified common salt, being added to two parts of dry snow or pounded ice, will sink the thermometer five degrees below zero. One part of sal-ammoniac, and two of common salt, joined to five parts of snow, will bring it seven degrees lower. But equal parts of the nitrate of ammonia and common salt, joined to two parts and a half of snow, will depress the thermometer 25 degrees below the freezing point.

Still more intense cold might be produced, if the ingredients were, before their mixture, cooled down to congelation. Thus, five parts of the muriate of lime, added to four parts of snow, will sink the thermometer to 40 degrees below the beginning of the scale, or the limit of freezing mercury; and, if the muriate of lime were crystallized, the effect would be 10 degrees more. The same extreme energy is exerted, on adding four parts of dry caustic potash to three parts of snow.

The mineral acids likewise, in a diluted state, produce similar effects. Two parts of weak sulphuric acid, joined to three of snow, will sink the thermometer to 23 degrees below zero. The muriatic and nitric acids, in nearly the same proportions, will depress it from 4 to 7 degrees more. By repeating the applications, therefore, a most intense cold may be created. Yet, to succeed completely, a skilful manipulation is required. The saline matters should be reduced to a fine powder, and the freezing mixtures should be made in very thin vessels, not larger than will barely hold them. In this way, by successive stages of cooling, Mr Walker once obtained the enormous cold of 91 degrees below the commencement of Fahrenheit's scale.

The mere evaporation of some very volatile liquids is sufficient to produce excessive cold. Thus, if a thermometer, having its bulb covered with lint, be dipped in the common or sulphuric ether, it will, on exposure to the air, sink perhaps 30 or 40 degrees. This effect is augmented under the receiver of an air-pump. If a narrow thin tube of glass, filled with water, and cased on the outside with lint soaked in ether, be suspended above the pump, and the exhaustion quickly made, a cylinder of ice will be formed.

The same property is manifested in a higher degree by a singular liquid, discovered by Lampadius in 1796, by distilling a mixture of pyrites and charcoal. It was called at first the alcohol of sulphur, but now more appropriately the sulphuret of carbon. According to Dr Marcet, who has completed the investigation of its properties, a thermometer having its bulb covered with lint wetted by this liquid, and held in the open air, will sink not fewer than 60 degrees. But if the same experiment be performed within the exhausted receiver of an air-pump, the alcohol of the barometer will even descend to 82 degrees below zero. It must be observed, however, that these effects produced by the evaporation of ether, and of the sulphuret of carbon, are quite evanescent, and that the receiver becomes soon charged with their fumes, which then prevent any farther action. Those fumes likewise corrode the valves of the pump, and soon render it quite useless. Neither ether, therefore, nor the sulphuret of carbon, could be applied in practice with any sort of advantage, to the production of ice, even on the smallest scale.

We have now to relate a discovery which will enable human skill to command the refrigerating powers of nature; and, by the help of an adequate machinery, to create cold and produce ice, on a large scale, at all seasons, and in the hottest climates of the globe. But, to explain this interesting subject with greater clearness and accuracy, it is requisite to trace the successive advances which conducted to the result. Where a conclusion appears simple, the careless observer is apt to suppose it easily attained; yet, though sound philosophy tends always to simplification, the rare quality of simplicity is scarcely ever the flash of intuition, but the slow fruit of close and patient investigation.

In pursuing the researches with his hygrometer, Professor Leslie was early induced to inquire into the condition of the higher atmosphere, and its relations

to humidity. He thus detected a fact of great importance in meteorology, and pointing at various ulterior views.

As rarefaction enlarges the capacity of air for heat, so it likewise augments the disposition to hold moisture; at the same time, that the removal of the ordinary pressure facilitates the expansion of the liquid matter, and its conversion into a gaseous form. Accordingly, if the hygrometer be suspended within a large receiver, from which a certain portion of air is quickly abstracted, it will sink with rapidity. In summer, the additional dryness thus produced amounts to about 50 hygroscopic degrees, each time the air has its rarefaction doubled; so that, supposing the operation of exhausting to be performed with expedition, and the residuum reduced to a sixty-fourth part, the hygrometer would mark a descent of 300°. But this effect is only momentary, for the thin air very soon becomes charged with moisture, and, consequently, ceases to act on the wet ball of the hygrometer. The cold, however, excited on the surface of that ball, by such intense evaporation, will have previously frozen the coating.

The increased power of aqueous solution which air acquires as it grows thinner, being ascertained and carefully investigated, the object was to combine the action of absorbent with the transient dryness produced within a receiver by rarefaction. The sentient ball of the hygrometer being covered with dry salt of tartar, the instrument first indicated increasing dryness, and afterwards, as the rarefaction proceeded, it changed its course, and marked humidity. The same variation of effect nearly was observed, when the hygrometer had been wetted as usual with pure water, and a broad saucer containing the mild vegetable alkali was placed on the plate of the air-pump. It was thus proved, that the action of this imperfect absorbent is soon overpowered by the tendency to vaporization in attenuated air, and that, beyond a certain limit, it surrenders its latent moisture.

Mr Leslie resolved, therefore, to try the effect of sulphuric acid, whose peculiar energy as an absorbent he had, under other circumstances, already ascertained. But various incidents prevented him, for a considerable time, from resuming his philosophical inquiries. At last he began those projected experiments, and was almost immediately rewarded by the disclosure of a property, the application of which blazed on his fancy. In the month of June 1810, having introduced a surface of sulphuric acid under the receiver of an air-pump, he perceived with pleasure that this substance only superadded its peculiar attraction for moisture, to the ordinary effects resulting from the progress of exhaustion; and, what was still more important, that it continued to support, with undiminished energy, the dryness thus created. The attenuated air was not suffered, as before, to grow charged with humidity; but each portion of that medium, as fast as it became saturated by touching the wet ball of the hygrometer, transported its vapour to the acid, and was thence sent back denuded of the load, and fitted again to renew its attack with fresh vigour. By this perpetual circulation, therefore, between the exhaling and the absorbing surface, the diffuse residuum of air

is maintained constantly at the same state of dryness. The sentient ball of the hygrometer, which had been covered with several folds of wetted tissue paper, was observed, at an early stage of the operation, suddenly to lose its blue tint and assume a dull white, while the coloured liquor sprung upwards in the stem, where it continued, for the space of a minute, stationary, and again slowly subsided. The act of congelation had, therefore, at this moment taken place, and the paper remained frozen several minutes, till its congealed moisture was entirely dispersed. Pursuing this decisive intimation, the hygrometer was removed, and a watch-glass filled with water substituted in its place. By a few strokes of the pump, the whole was converted into a solid cake of ice, which, being left in the rare medium, continued to evaporate, and, after the interval of perhaps an hour, totally disappeared. A small cup for holding the water was next adopted, and the whole apparatus gradually enlarged.

The powers, both of vaporization and of absorption, being greatly augmented in the higher temperatures, the same limit of cold nearly is in all cases attained, by a certain measure of exhaustion. When the air has been rarefied 250 times, the utmost that, under such circumstances, can perhaps be effected, the surface of evaporation is cooled down 120 degrees of Fahrenheit in winter, and would probably sink near 200 in summer. Nay, a far less tenuity of the medium, when combined with the action of sulphuric acid, is capable of producing and supporting a very intense cold. If the air be rarefied only 50 times, a depression of temperature will be produced, amounting to 80 or even 100 degrees of Fahrenheit's scale.

We are thus enabled, in the hottest weather, to freeze a mass of water, and to keep it frozen, till it gradually wastes away, by a continued but invisible process of evaporation. The only thing required is, that the surface of the acid should approach tolerably near to that of the water, and should have a greater extent, for otherwise the moisture would exhale more copiously than it could be transferred and absorbed, and, consequently, the dryness of the rarefied medium would become reduced, and its evaporating energy essentially impaired. The acid should be poured to the depth perhaps of half an inch in a broad flat dish, which is covered by a receiver of a form nearly hemispherical; the water exposed to congelation may be contained in a shallow cup, about half the width of the dish, and having its rim supported by a narrow porcelain ring upheld above the surface of the acid by three slender feet. (See fig. 1 and 2. Plate LXV.) It is of consequence that the water should be insulated as much as possible, or should present only a humid surface to the contact of the surrounding medium, for the dry sides of the cup might receive, from communication with the external air, such accessions of heat, as greatly to diminish, if not to counteract the refrigerating effects of evaporation. This inconvenience, however, is in a great measure obviated, by investing the cup with an outer case at the interval of about half an inch. If both the cup and its case consist of glass, the process of congelation is viewed most completely; yet when they are formed of a bright metal, the effect

appears on the whole more striking. But the preferable mode, and that which prevents any waste of the powers of refrigeration, is to expose the water in a pan of porous earthen-ware. If common water be used it will evolve air bubbles very copiously as the exhaustion proceeds; in a few minutes, and long before the limit of rarefaction has been attained, the icy spicule will shoot beautifully through the liquid mass, and entwine it with a reticulated texture. As the process of congelation goes forward, a new discharge of air from the substance of the water takes place, and marks the regular advances of consolidation. But after the water has all become solid ice, which, unless it exceed the depth of an inch, may generally be effected in less than half an hour, the circle of evaporation and subsequent absorption is still maintained. A minute film of ice, abstracting from the internal mass a redoubled share of heat, passes, by invisible transitions, successively into the state of water and of steam, which, dissolving in the thin ambient air, is conveyed to the acid, where it again assumes the liquid form, and, in the act of combination, likewise surrenders its heat.

In performing this experiment, the object is generally to seek at first to push the rarefaction as far as the circumstances will admit. But the disposition of the water to fill the receiver with vapour, being only in part subdued by the action of the sulphuric acid, a limit is soon opposed to the progress of exhaustion, and the included air can seldom be rarefied above a hundred times, or till its elasticity can support no more than a column of mercury about three tenths of an inch in height. A smaller rarefaction, perhaps from ten times to twenty times, will be found sufficient to support congelation after it has once taken place. The ice then becomes rounded by degrees at the edges, and wastes away insensibly, its surface being incessantly corroded by the play of the ambient air, and the minute exhalations conveyed by an invisible process to the sulphuric acid, which, from its absorbing the vapour, is all the time maintained above the temperature of the apartment. The ice, kept in this way, suffers a very slow consumption; for a lump of it, about a pound in weight and two inches thick, is sometimes not entirely gone in the space of eight or ten days. During the whole progress of its wasting, the ice still commonly retains an uniform transparent consistence; but, in a more advanced stage, it occasionally betrays a sort of honey-combed appearance, owing to the minute cavities formed by globules of air, set loose in the act of freezing, yet entangled in the mass, and which are afterwards enlarged by the erosion of the solvent medium.

But almost every practical object is attained, through far inferior powers of refrigeration. Water is the most easily frozen, by leaving it, perhaps for the space of an hour, to the slow action of air that has been rarefied only in a very moderate degree. This process meets with less impediment, and the ice formed by it appears likewise more compact, when the water has been already purged of the greater part of its combined air, either by distillation or by long continued boiling. The water which has undergone such operation, should be introduced as

quickly as possible into a decanter, and filled up close to the stopper, else it will attract air most greedily, and return nearly to its former state in the course of a few hours.

The most elegant and instructive mode of effecting artificial congelation, is to perform the process under the transferer of an air-pump. A thick but clear glass cup being selected, of about two or three inches in diameter, has its lips ground flat, and covered occasionally, though not absolutely shut, with a broad circular lid of plate glass, which is suspended horizontally from a rod passing through a collar of leather. (See fig. 6. Plate LXV.) This cup is nearly filled with fresh distilled water, and supported by a slender metallic ring, with glass feet, about an inch above the surface of a body of sulphuric acid, perhaps three quarters of an inch in thickness, and occupying the bottom of a deep glass bason that has a diameter of nearly seven inches. In this state, the receiver being adapted, and the lid pressed down to cover the mouth of the cup, the transferer is screwed to the air-pump, and the rarefaction, under those circumstances, pushed so far as to leave only about the hundred and fiftieth part of a residuum; and the cock being turned to secure that exhaustion, the compound apparatus is then detached from the pump, and removed to some convenient apartment. As long as the cup is covered, the water will remain quite unaltered; but, on drawing up the rod half an inch or more, to admit the play of the rare medium, a bundle of spicular ice will, after the lapse perhaps of five minutes, dart suddenly through the whole of the liquid mass; and the consolidation will afterwards descend regularly, thickening the horizontal stratum by insensible gradations, and forming in its progress a beautiful transparent cake. On letting down the cover again, the process of evaporation being now checked or almost entirely stopped, the ice returns slowly into its former liquid condition. In this way, the same portion of water may, even at distant intervals of time, be repeatedly congealed and thawed successively twenty or thirty times. During the first operations of freezing, some air is liberated; but this extrication diminishes at each subsequent act, and the ice, free from the smallest specks, resembles a piece of the purest crystal.

and forms by congelation a regular pyramid, rising by successive steps; or, if the projecting force be greater, and the hole more contracted, it will dart off like a pillar. The radiating or feathered lines which at first mark the frozen surface, are only the edges of very thin plates of ice, implanted at determinate angles, but each parcel composed of parallel planes. This internal formation appears very conspicuous in the congealed mass which has been removed from a metallic cup, before it is entirely consolidated.—Sea-water will freeze with almost equal ease, but it forms an incompact ice like congealed syrup, or what is commonly called water-ice.

When cups of glass or metal are used, the cold excited at the open surface of the liquid extends its influence gradually downwards. But if the water be exposed in a porous vessel, the process of evaporation, then taking effect on all sides, proceeds with a nearly regular consolidation towards the centre of the mass, thickening rather faster at the bottom from its proximity to the action of the absorbent, and leaving sometimes a reticulated space near the middle of the upper surface, through which the air, disengaged by the progress of congelation, makes its escape.

When very feeble powers of refrigeration are employed, a most singular and beautiful appearance is, in course of time, slowly produced. If a pan of porous earthen-ware, from four to six inches wide, be filled to the utmost with common water till it rise above the lips, and planted above a dish of ten or twelve inches diameter, containing a body of sulphuric acid, and then a broad round receiver placed over it; on reducing the included air to some limit between the twentieth and the fifth part of its usual density, according to the coldness of the apartment, the liquid mass will, in the space of an hour or two, become entwined with icy shoots, which gradually enlarge and acquire more solidity, but always leave the fabric loose and unfrozen below. The icy crust which covers the rim, now receiving continual accessions from beneath, rises perpendicularly by insensible degrees. From each point on the rough surface of the vessel, filaments of ice, like bundles of spun glass, are protruded, fed by the humidity conveyed through its substance, and forming in their aggregation a fine silvery surface, analogous to that of fibrous gypsum or satin-spar. At the same time, another similar growth, though of less extent, takes place on the under side of the pan, so that continuous icy threads might appear vertically to transpierce the ware. The whole of the bottom becomes likewise covered over with elegant icy foliations. (See fig. 5.) Twenty or thirty hours may be required to produce those singular effects; but the upper body of ice continues to rise for the space of several days, till it forms a circular wall of near three inches in height, leaving an interior grotto lined with fantastic groups of icicles. In the meanwhile, the exfoliations have disappeared from the under side, and the outer incrustation is reduced, by the absorbing process, to a narrow ring. The icy wall now suffers a regular waste from external erosion, and its fibrous structure becomes rounded and less apparent. Of its altitude, however, it loses but little for some time; and even a deposition of congealed films along its coping or upper edge, seems to take place, at a certain stage of the process.

This artificial freezing of water in a cup of glass or metal, affords the best opportunity of examining the progress of crystallization. The appearance presented, however, is extremely various. When the frigorific action is most intense, the congelation sweeps at once over the whole surface of the water, obscuring it like a cloud. But, in general, the process advances more slowly; bundles of spiculæ, from different points, sometimes from the centre, though commonly from the sides of the cup, stretching out and spreading by degrees with a sort of feathered texture. (See fig. 4.) By this combined operation, the surface of the water soon becomes a uniform sheet of ice. Yet the effect is at times singularly varied; the spicular shoots, advancing in different directions, come to inclose, near the middle of the cup, a rectilinear space, which, by unequal though continued encroachment, is reduced to a triangle; and the mass below, being partly frozen, and therefore expanded, the water is gradually squeezed up through the orifice,

Cold. This curious effect is owing to a circumstance, which as it serves to explain some of the grand productions of nature, particularly the Icebergs of the Arctic Circle, merits particular attention. The circular margin of the ice, being nearer the action of the sulphuric acid than its inner cavity, must suffer, by direct evaporation, a greater loss of heat; and, consequently, each portion of thin air that rises from the low cavity, being chilled in passing over the colder ledge, must deposit a minute corresponding share of its moisture, which instantly attaches itself and incrusts the ring. Whatever inequalities existed at first in the surface of the ice, will hence continually increase.

Artificial congelation is always most commodiously performed on a large scale. Since the extreme of rarefaction is not wanted, the air-pump employed in the process admits of being considerably simplified, and rendered vastly more expeditious in its operation: Two or three minutes at most will be sufficient for procuring the degree of exhaustion required, and the combined powers of evaporation and absorption will afterwards gradually produce their capital effect. In general, plates of about a foot in diameter should be preferred, which can be connected at pleasure with the main body of the pump. The dish holding the sulphuric acid is nearly as wide as the flat receiver; and a set of evaporating pans belongs to it, of different sizes, from seven to three inches in diameter, which are severally to be used according to circumstances. The largest pan is employed in the cold season, and the smaller ones may be successively taken as the season becomes sultry. On the whole, it is better not to overstrain the operation, and rather to divide the water under different receivers, if unusual powers of refrigeration should be required. As soon as the air is partly extracted from one receiver, the communication is immediately stopped with the barrel of the pump, and the process of exhaustion is repeated on another. In this way, any number of receivers, it is evident, may be connected with the same machine. If we suppose but six of these to be used, the labour of a quarter of an hour will set as many evaporating pans in full action, and may, therefore, in less than an hour afterwards produce nearly six pounds of solid ice. The waste which the water sustains during this conversion is extremely small, seldom indeed amounting to the fiftieth part of the whole. Nor, till after multiplied repetitions, is the action of the sulphuric acid considerably enfeebled by its aqueous absorption. At first that diminution is hardly perceptible, not being the hundredth part when the acid has acquired as much as the tenth of its weight of water. But such influence gains rapidly, and rises with accelerated progression. When the quantity of moisture absorbed amounts to the fourth part by weight of the acid, the power of supporting cold is diminished by a twentieth; and, after the weights of both these come to be equal, the refrigerating energy is reduced to less than the half. Sulphuric acid is hence capable of effecting the congelation of more than twenty times its weight of water, before it has imbibed near an equal bulk of that liquid, or has lost about the eighth part of its refrigerating power. The acid should then be removed, and concentrated anew by slow distillation.

When the exhaling and absorbing surfaces are rightly disposed and apportioned, the moderate rarefaction, from twenty to forty times, which is adequate to the freezing of water, may be readily procured by the condensation of steam. In all manufactures where the steam-engine is employed, ice may, therefore, at all times be formed in any quantity, and with very little additional expence. It is only required to bring a narrow pipe from the condensing vessel, and to direct it along a range of receivers, under each of which the water and the acid are severally placed. These receivers, with which the pipe communicates by distinct apertures, may, for the sake of economy, be constructed of cast-iron, and adapted with hinges to the rim of a broad shallow dish of the same metal, but lined with lead to hold the acid.

The combined powers of rarefaction and absorption are capable of generating much greater effects than the mere freezing of water. Such frigorific energy, however, is at all times sufficient for effecting the congelation of mercury. Accordingly, if mercury, contained in a hollow pear-shaped piece of ice, be suspended by cross threads near a broad surface of sulphuric acid under a receiver; on urging the rarefaction, it will become frozen, and may remain in that solid state for the space of several hours. But this very striking experiment is easily performed without any foreign aid. Having introduced mercury into the large bulb of a thermometer, and attached the tube to the rod of a transferer, let this be placed over the wide dish containing sulphuric acid, in the midst of which is planted a very small tumbler nearly filled with water: After the included air has been rarefied about fifty times, let the bulb be dipped repeatedly into the very cold but unfrozen water, and again drawn up about an inch; in this way, it will become incrustated with successive coats of ice, to the thickness perhaps of the twentieth part of an inch: The water being now removed, the pendant icicle cut away from the bulb, and its surface smoothed by the touch of a warm finger, the transferer is again replaced, the bulb let down within half an inch of the acid, and the exhaustion pushed to the utmost: When the syphon-gage has come to stand under the tenth of an inch, the icy crust starts into divided fissures, and the mercury, having gradually descended in the tube till it reach its point of congelation, or 39 degrees below zero, sinks by a sudden contraction almost into the cavity of the bulb; and the apparatus being then removed and the bail broken, the metal appears a solid shining mass, that will bear the stroke of a hammer.

But a still greater degree of cold may be created, by applying the same process likewise to cool the atmosphere which encircles the apparatus itself. A glass matrass was blown nearly of a hemispherical shape, its bottom quite flat, and about three inches in diameter, and its neck about half an inch wide and cut square over: The whole was covered with a coat of patent lint, which takes up water very copiously, a portion of sulphuric acid was next introduced, forming a layer of perhaps a quarter of an inch thick, and a spirit of wine thermometer, having its bulb also cased with wetted lint, was then inserted within the matrass, a brass ring attached to the tube securing it in the

right position. Things being thus arranged, the mattress or flat bottle, with its thermometer, was placed on a slender stool with glass feet, about an inch above the sulphuric acid in the broad bason, and the large receiver luted over it. The air was then partly extracted, till the gage came below one inch: In a few minutes, the lint was frozen entirely, and looked white. After an interval of a quarter of an hour, to allow time for the evaporation of that icy coat to cool down the interior apparatus, the pump was again urged, and the exhaustion pushed to about three-tenths of an inch. In a short while, the inclosed thermometer sunk not fewer than 180 degrees, and remained stationary, till the ice had wasted away.

It is obvious, therefore, that the refrigerating powers could be pushed still farther by a judicious combination of the apparatus. An idea of the mode of proceeding may be formed from the inspection of figure 8. It would be easy to show, that the maximum effect is obtained, when the dimensions of the successive cases rise in a geometrical progression. The action, however, is not doubled for each additional case, but increased rather more than one-half.

These plans are difficult in the execution, and though they enlarge our conceptions of the extent of the descending scale of heat, yet they furnish merely speculative results. A very important practical improvement has been lately made in the process of artificial congelation. Sulphuric acid is certainly a cheap and most powerful agent of absorption; but the danger in using such a corrosive liquid, especially by unskilful persons, formed always

a serious obstacle to its general adoption. Mr Leslie had early noticed the remarkable absorbent quality of our mouldering whinstone or porphyritic trap; and, in April 1817, he substituted that material, grossly pounded and dried before a kitchen fire, instead of sulphuric acid, and actually froze a body of water with great facility. This earth will attract the fiftieth part of its weight of moisture before its absorbent power is reduced to the one half, and is hence capable of freezing the sixth part of its weight of water. It may be repeatedly dried, and will, after each operation, act with the same energy as at first.

But an absorbent still more convenient and powerful has since occurred to Mr Leslie:—it is merely or Parched oatmeal. With a body of oatmeal of a foot in diameter, and rather more than an inch deep, he froze a pound and a quarter of water, contained in a hemispherical porous cup. The meal is easily dried and restored again to its action. In a hot climate, the exposure to the sun alone might prove sufficient. By the help of this simple material, therefore, ice will be easily and safely produced in any climate, and even at sea.

Other substances could, no doubt, be employed as absorbents. But, except the muriate of lime, or what is called the oil of salt desiccated, none hold out any prospect of success. Dried common salt will barely effect congelation; and stucco, or the sulphate of lime, deprived of its water of crystallization, which might seem to promise a powerful absorption, has scarcely any efficacy whatever. (D.)

EXPLANATION OF PLATE LXV.

Fig. 1. Represents a large air-pump intended for the purpose of freezing water, consisting of six receivers, each of them having a broad glass saucer for holding sulphuric acid, and a small porous earthen cup containing the water.

Fig. 2. A section of the above, showing the communication between the receivers and the body of the pump.

Fig. 3. The lever key, for opening and shutting the cocks.

Fig. 4. The more ordinary appearance of the surface of the water in the porous cup, at the moment when the act of congelation begins.

Fig. 5. The very singular kind of ice, striated, columnar, and cavernous, which, under a slight rarefaction, but in cold weather, rises slowly and changes its form by degrees, while part of the remaining water is drawn through the substance of the cup, and covers the outside with a thick icy collar above those irregular foliations.

Fig. 6. Represents an elegant mode of almost instantaneous freezing within a transferer; above the saucer of the sulphuric acid, is placed a glass cup holding water, and the air having been previously exhausted, and the instrument detached from the pump, on pulling up the rod, the water, now left ex-

posed to the most powerful evaporation, quickly runs into spicular ice, which gradually increases and consolidates into a pure transparent mass. The lid being let down again upon the glass cup, the action ceases, and the ice returns slowly to the state of water.

Fig. 7. A refrigeratory for cooling water at all times to a moderate degree, without the operation of an air-pump; a body of sulphuric acid lying at the bottom of the pan, while a porous vessel containing water is set in the centre of the refrigeratory, and the air is confined about it by replacing the lid.

Fig. 8. Exhibits a system of vessels for producing spontaneously great cold. It consists of a series of leaden or pewter vessels, placed one within the other, and whose surfaces form a descending geometrical progression, being covered externally with soft wet lint, and holding each of them a portion of sulphuric acid. The powerful evaporation maintained by this arrangement causes the interior vessels to become successively colder, and thus augments, by a repeated multiplication, the final effect. Placed under the receiver of the air-pump, this system of evaporating vessels, with no very high degree of exhaustion, and at all seasons, excites ultimately the most intense cold yet produced, far exceeding what is required for the congelation of mercury.

♠ A number of the machines here described have been constructed, under the direction of the inventor, by Mr Cary, Optician, London, and sent to various parts of the Globe. It is only to be regretted, that the demand has not been sufficient for establishing a manufactory of them, which, by greatly reducing the cost, would encourage their general introduction.

COLD.

PROFESSOR LESLIE'S APPARATUS FOR COOLING AND FREEZING.
Fig. 5.

PLATE LXV.

Fig. 4.

Fig. 7.

Fig. 2.

Fig. 5.

Fig. 6.

Fig. 1.

Fig. 3.