(fig. 11.) represents a glass cylinder, twelve inches in diameter and the same in height, covered by a glass plate fitted to it by a projecting fillet on the under surface. This cover is pierced with two round holes one inch and three fourths in diameter. One of them is in the centre, and receives the lower end of the glass tube fh, of twenty-four inches height, which is fixed in the hole with a cement made of sealing-wax, or other electric substance. The top of this tube receives the brass collar H, (fig. 12. No. 3.) bored truly cylindrical with a small shoulder, which rests on the top of the tube. This collar is fastened with cement, and receives the hollow cylinder φ (fig. 12. No. 2.), to which is joined the circular plate ab, divided on the edge into 360 degrees. It is also pierced with a round hole G in the centre, which receives the cylindrical pin i (fig. 12. No. 1.) having a milled head b, and furnished with an index io, whose point is bent down so as to mark the divisions on the circle ab. This pin turns freely in the hole G, and the cylinder φ moves readily in the collar H. To the lower end of the centre pin is fastened a little pincer, q, formed like the end of a port-crayon, and tightened by the ring r, so as to hold fast the suspension wire, the lower end of which is grasped by a similar pincer, P o (fig. 13.) tightened by the ring φ. The lower end φ o is cylindrical, and is of such a weight, as to draw the wire perfectly straight, but without any risk of breaking it. It may be made equal to half of the weight that will just break it.

This pincer is enlarged at C, and pierced with a hole, which tightly receives the arm g C q of the electrometer. This arm is eight inches long; and consists of a dry silk thread, or a slender straw completely dried, and dipped in melted lac or fine sealing wax, and held perpendicularly before a clear fire, till it become a slender cylinder of about one tenth of an inch in diameter. This occupies six of the eight inches, from g to q; the remaining two inches consist of a fine thread of the lac or sealing-wax, as it drains off in forming the arm. At a, is a ball of pitch or fine cork, one-fourth or one-half of an inch in diameter, made very smooth, and gilded. It is balanced by a vertical circle of paper g, of large dimensions, made stiff with varnish. The refraction of the air to this plane soon checks the oscillations of the arm.

The whole instrument is seen in its place in fig. 11, where the arm hangs horizontally about the middle of the height of the great cylinder. In its oscillations the ball a moves round in a circle, whose centre is in the axis of the whole instrument. Its situation is indicated by a graduated circle zoq, drawn on a slip of paper, and made to adhere to the glass by varnish. The electrified body whose action is to be observed, is another small ball of cork t, also gilt, or a brass ball well polished. This is carried by a stalk of lac m φ, inclosing a dry silk thread. This stalk is grasped by a clamp of cleft deal, or any similar contrivance, which is made to lie firm on the glass cover. When this ball is let down through the hole m, it stands so as to touch the ball a on the arm, when that ball is opposite to o on the graduated circle.

In order to electrify the ball t, we are to employ the insulating handle, fig. 14, which is a slender stick of sealing-wax or lac, holding a metal wire that carries a small polished metallic ball. This is to be touched with some electrified body, such as the prime conductor of a machine, the knob of a jar, &c. This electrified ball is to be introduced cautiously into the hole m, and the ball t is to be touched with it. The ball a is immediately repelled to a distance, twisting the suspension wire, till the force of twist exerted by the wire balances the mutual repulsion of the balls t and a.

This is the process for examining the law of electric action. When it is desired to examine the action of different bodies in different states, another apparatus is wanted. This is represented by the piece c A d (fig. 15.) consisting of a plug of sealing-wax A, fitting tightly into the hole m, and pierced by the wire c d, hooked at c, to receive a wire to connect it occasionally with an electrified body, and having below a polished metal ball d.

The instrument is fitted for observation in the following manner: The milled button b is turned at top, till the twist index io is at the mark o of the twist circle. Then the whole is turned in the collar H, till the ball a stand opposite to the mark o of the paper circle zoq, and at the same time the ball t or d is touched. The observation is thus made. The ball t is first electrified, as just described, and thus a is repelled, and retiring twists the wire, settling, after a few oscillations, at such a distance as is proportional to the repulsion. The twist-index is now turned so as to force a nearer to t. The repulsion thus produced is estimated by adding the motion of the index to the angle at which the ball first stopped. Giving the index another, we have another repulsion, which is estimated in a similar way, and thus we obtain as many measures as required.

It is not necessary to make this instrument of very large dimensions; one 14 inches high, and five in diameter, of which the arm ag should occupy two inches and a half, will be sufficiently large for most purposes. The diameter of the glass cylinder must always be double the length of the arm ag, that the position of this may not be disturbed by the action of the glass.

Dr Robison considered this electrometer as one of the Electrometers are the most valuable instruments that have been made, as it is not only extremely delicate, but gives absolute measures with the greatest accuracy. For all purposes in which only repulsions were to be measured, he preferred it to his own instrument described in Electricity, No. 206.

He, however, suggested several improvements in it, which are deserving of attention.

The bottom should be furnished with a round hole, admitting the lower end of the cylinder Cc belonging to the lower pincer (when the wire is strained at both ends) to hang freely, by which means much tedious oscillation will be prevented. It is much more convenient to have the suspension wire strained at both ends; and it should extend as far below the arm as above it; and the lower extremity should be grasped by a pincer that turns by a milled head in a hole at the end of a slender spring. The instrument may then be speedily adjusted by placing the twist index at o, and gently turning the lower button till the ball a point exactly at o on the paper circle.

The instrument will be greatly improved, if, in place of the apparatus with the ball a, we substitute the piece represented at fig. 15, making some little changes in its construction. Thus, instead of the wire cd, is used the smallest glass tube that will admit of being varnished on the inside, which is done by drawing through it a silk thread dipped in varnish, made of lac.

The outside of the tube must also be varnished, and a brass ball d fixed at its lower end, and a slender wire, furnished with a ball, is to be inserted into the tube, so as to touch the ball below. The position of the ball d will not be liable to alteration, when the hole m is once stopped with the plug. In making delicate experiments, the upper ball c, must be touched with the charger, represented at fig. 14, by which means the ball d is electrified. Then drawing out C by means of the forceps, the ball d is left completely inflated. In examining the electricity of the atmosphere, to which purpose this instrument is well adapted, the wire must be allowed to remain in the tube.

It was by means of this incomparable instrument, that M. Coulomb made the valuable experiments, to which we alluded in the article Electricity, when treating of the law of action of the electric fluid. By means of this electrometer, he also made his experiments on the dissipation of electricity into the air, and along imperfect conductors. He ascertained the law of dissipation into the air from bodies in contact, and the relation which this bore to the original repulsion, by first observing the gradual approach of the ball a towards t, in proportion as the electricity dissipated from both, and then slackening the twist index till the ball a resumed its original situation.

The following was the general result of Mr Coulomb's experiments.

That the momentary dissipation of moderate degrees of electricity is proportional to the degree of electricity at the moment. He found that the dissipation is not sensibly affected by the state of the barometer or thermometer; nor is there any sensible difference of bodies of different sizes or different substances, or even different figures, provided that the electricity is very weak.

But he found that the dissipation was greatly affected by the different states of humidity of the air. In the Electrometer scale of Saufure's hygrometer, the relation to the quantity of water which a cubic foot of air is capable of holding in solution is distinctly marked; the relation of this solution to the dissipation of electricity in Coulomb's experiments may hence be seen in the following table, the first column of which marks the degrees of Saufure's hygrometer, the second how many grains of water are dissolved in a cubic foot of air at each degree, and the third column shows the corresponding dissipation per minute.

| Degrees | Grains of Water | Dissipation | |---------|-----------------|-------------| | 69 | 6.197 | 3/8 | | 75 | 7.295 | 4/8 | | 80 | 8.045 | 5/8 | | 87 | 9.221 | 7/8 |

Hence it follows, that the dissipation is very nearly in the triplicate ratio of the moisture of the air. Thus if we make \( \frac{6}{7} = \frac{7.197}{6.180} \); \( m \) will be \( 2.764 \). If we make \( \frac{6}{7} = \frac{8.045}{6.180} \); \( m \) will be \( 2.76 \); and if we make \( \frac{6}{7} = \frac{9.240}{6.180} \); \( m \) will be \( 3.61 \); or at a medium \( m \) will be \( 3.40 \).

The immediate object, that M. Coulomb had in view in his experiments, was to ascertain the diminution of repulsion. He found that this, in a given state of the air, was a certain proportion of the whole repulsion taken at the moment of diminution, which is double the proportion of the density of the fluid; for the repulsions by which we judge of the dissipation are reciprocal, being exerted by every particle of fluid in the ball t of the electrometer, on every particle of fluid in the ball a. The diminution of repulsion is therefore proportional to the density of the electric fluid in each ball; and, as during the whole dissipation, the densities continue to have their original proportion, and as the diminution of repulsion is directly proportional to the diminution of the products of the densities, it is consequently directly proportional to the square of either. If we put \( d \) for the density, the mutual repulsion will be represented by \( d^2 \), and its momentary diminution by the fluxion of \( d^2 \), or \( 2d \times d \). But \( 2d \times d : d^2 = 2d : a \). The diminution of repulsion observed by experiment will be to the whole repulsion, in double the proportion that the diminution of density, or the dissipation of fluid will have to the whole quantity of fluid at the moment of observation.

Let us, for instance, suppose the observed diminution of repulsion to be \( \frac{1}{8} \); we may conclude, that the quantity of fluid lost by dissipation is \( \frac{1}{8} \). M. Coulomb did not examine the proportion of the dissipations from bodies of various sizes. But we know, that if two spheres communicate by a very long canal, their superficial densities, and the tendencies of fluid to escape from them, are inversely as the diameters of the spheres. Now, in a body that has twice the diameter of another body, the surface of the former is quadruple of that of the latter; and though the tendency of fluid to escape from the former is only the half of its tendency to escape from the latter, yet the greater surface of the former may so far make up for its smaller density, that the Electromagnetic diffusion of fluid from a large sphere may in fact be greater than that from a small one in the same given time.

We have remarked above, that these experiments were made in a particular state of the air; and the law of diffusion ascertained by them is of course adapted only to that given state. In a different state of the air, even if this should be impregnated with the same proportion of moisture, the law of diffusion may be different. The inference which M. Coulomb expected to draw from his experiments was, that the ratio of diffusion would prove to be less than the cube of the quantity of water held in solution, except when that quantity of water was what the air was capable of holding in solution at the given temperature.

This is agreeable to observation; for we know that air which is considered as dry, that is, when it is not nearly saturated with moisture, is the most favourable to electrical phenomena.

Such is the general result of Coulomb's experiments on the diffusion of electricity into the air.

The method in which M. Coulomb examined the diffusion along imperfect conductors, by means of this instrument, was by completely inflating the ball, and then, after observing the loss sustained by a body in contact with it from the air, sliding a metallic rod down the inflating stalk, till the diffusion began to exceed what took place only by the air.

From his experiments respecting the diffusion along imperfect conductors, he found that this took place in a different manner from that in which electricity escaped by communication with the contiguous air. The electricity seems to be diffused chiefly along the surface of the insulator, and appears principally to be produced by the moisture that is more or less attached to it. M. Coulomb illustrates this in the following manner.

Water is found to adhere to the surface of all bodies, from which it is prevented by adhesion from escaping when the bodies are electrified, and is thus rendered capable of receiving a greater degree of electric power. Let us suppose that the particles of moisture are disposed uniformly over the surface, with intervals between them; the electricity that is communicated to one particle, must acquire a certain degree of density, before it can fly from this particle to the next, across the intervening insulating space. When an imperfect conductor of this kind is electrified at one extremity, the communicated electricity, in passing to the other extremity, must be weakened every step in passing from particle to particle.

Suppose we have three adjacent particles, which we may call \(a\), \(b\), and \(c\); we infer from No. 374 of the article Electricity, that the motion of \(b\) is lendly effected, only by the difference of \(a\) and \(c\); and therefore the passage of electric fluid from \(b\) to \(c\), requires that this difference be superior, or at least equal to the force necessary for clearing this coercive interval. Let a particle pass over. The density of fluid of the particle \(b\) is diminished, while the density of the particle on the other side of \(a\) remains as before. Therefore some fluid will pass from \(a\) to \(b\), and from the particle preceding \(a\) to \(a\); and so on, till we come to the electrified end of this insulator. It is plain, from this consideration, that we must at last arrive at a particle beyond \(c\), where the whole repulsion of the preceding particle is just sufficient to clear the coercive interval. Some fluid will come over; and the repulsion of this, acting now in the opposite direction, will prevent any fluid from coming to supply its place in the particle which it has just quitted; the transference of fluid will therefore stop here, and beyond this point the inflation will be complete. Hence we perceive that there is a mathematical relation between the inflating power, and the length of the canal; and this may be determined by the theory which we adopted in the article Electricity. We shall here give an instance of this investigation; and, for the sake of simplicity, we shall take a very probable case, viz. where the inflating interval, or, as we may more properly call it, the coercive interval, is equal in every part of the canal.

Let \(R\) represent the coercive power of the insulator, or the degree of force required to clear the coercive interval between two particles. Suppose a ball \(C\), fig. 16, suspended by a silk thread \(AB\); and let us denote the quantity of redundant fluid in the ball by \(C\), and let the densities at the different points of the canal be denoted by \(AD\), \(PD\), &c., ordinates to some curve \(D'B\), cutting the axis in \(B\), the point where the thread \(AB\) begins to inflate completely. Let \(PP'\) be an element of the axis; draw the ordinate \(P'f\), a tangent to the curve \(D'F\), the normal \(D'E\), and draw \(f'e\) perpendicular to \(PD\). Suppose \(AC=x\), \(AP=x\), and \(PD=y\). Then we shall have \(PP=x\), and \(de=-y\). It was shown in No. 374 of the article Electricity, that the only sensible action of the fluid on a particle at \(P\) is \(-\frac{yy}{x}\), when the action of the redundant fluid in the globe on the particle at \(P\), having the density \(y\), is denoted by \(\frac{Cy}{(r+x)^2}\). Therefore \(-\frac{yy}{x}\) is \(=R\), the coercive power of the thread, which is supposed to be constant, \(\frac{PD\times de}{PP'}\) is therefore equal to some constant line \(R\). But \(PP'\) (or \(f'e\)) : \(de = PD : PE\). The subnormal \(PE\), is therefore a constant line. But as this is the property of a parabola, the curve of density \(D'B\) must be a parabola, of which \(2PE = 2R\), is the parameter.

Cor. 1.—The densities at different points of an imperfect insulator are in the subduplicate ratio of their distances from the point of complete inflation: for \(PD : AD^2 = BP : BA\).

Cor. 2.—The lengths of canal requisite for insulating different densities of the electric fluid are in the duplicate ratio of their densities; for \(AB = \frac{AD^2}{2PE}\), and \(PE\) is a constant quantity.

Cor. 3.—The length of canal requisite for insulation is inversely as its coercive power, and may be represented by \(\frac{D^2}{R}\). For \(AB = \frac{DA^2}{2PE} = \frac{D^2}{2R}\).

If we reflect on this theory, we shall perceive, that our formulæ determine the distribution of fluid along the surface of an imperfect conductor, only in a certain manner, supposing that the ball \(C\) has received a certain determinate portion of fluid, for this portion diffusing itself, particle by particle, through the conducting matter, will extend to \(b\) in such a manner, as that Electromagnetic repulsion shall be everywhere in equilibrium with the coercive power of the insulating interval, taken at a maximum. We must here remark that this resistance is not active, but only coercive, and may be compared to the resistance afforded by viscosity or friction. Any repulsion of electric fluid, which falls short of this, will not disturb the stability of the fluid that is spread along the canal, according to any law whatever. So that if \( AD \) represent the electric density of the globe, and remain constant, any curve of density will answer provided that \( \frac{d^2}{x} \) be everywhere less than \( R \). It is therefore an indeterminate problem, to assign in general the disposition of fluid in the canal. The density is as the ordinates of a parabola on this supposition only that the maximum of \( R \) is everywhere the same. And, in this case, the distance \( AB \) is a minimum; for, in other cases of density we must have \( \frac{d^2}{x} \) less than \( R \). If, therefore, we vary a single element of the curve \( D d B \), in order that the stability of the fluid may not be disturbed, having \( d \) constant, we must necessarily have \( x \) larger, that \( \frac{d^2}{x} \) may still be less than \( R \); that is, we must lengthen the axis.

The reasonings which have thus been deduced from theory, were confirmed by M. Coulomb in a numerous set of experiments. These are chiefly valuable for having stated the relation that subsists between the electric density, and the length of support necessary for complete insulation. But as M. Coulomb has not given us the scale of his electrometer, according to which the absolute measures of the densities were determined, the experiments can be of but little use till this be known.

We hinted, at the end of the theoretical part of Electricity, that the theory of Volta's condenser might be more satisfactorily explained after we had considered the above experiments of Coulomb. The account which we gave of the condenser in Chap. xiii. of that article, (chiefly from Cavallo), was the only one we could properly give in that early part of our view of the science. We are now prepared for a more scientific account of the effects of that instrument. The following is nearly the manner in which Dr Robison considered the subject.

Let the cover of an electrophorus be furnished with a graduated electrometer, such as may indicate the proportional degrees of electricity; electrify it positively to any degree, we shall suppose fix, while it is held in the hand, at a little distance, directly over a metallic plate lying on a wine glass, or such like insulating stand, but made to communicate with the ground by a wire. Now bring it gradually down towards the plate. Theory teaches, and we see it confirmed by experiment, that the electrometer will gradually subside, and will perhaps fall to \( 2^\circ \), before the electricity is communicated in a spark; but let us stop it before this happens; the attraction of the lying plate produces a compensation of four degrees of the mutual repulsion of the parts of the cover, by condensing the fluid on its inferior surface, and forming a deficient stratum above. This needs no farther explanation, after what we said under Electricity, on the charging of coated glass plates. Now we may suppose that the escape of the fluid from this body into the air begins as soon as it is electrified to \( 6^\circ \), and that it will fly to the insulated plate with the degree 2, if it be brought nearer. But if we can prevent this communication to the insulated plate, by interpolating an electric, we may electrify the cover again, while so near the metallic plate, to \( 6^\circ \), before it will pass off into the air. If now it be removed from the lying plate, the fluid would cause the electrometer to rise to \( 10^\circ \), if it did not immediately pass off; and an electric excitement of any kind which could raise this body only to \( 6^\circ \) by its intensity, will, by means of this apparatus, raise it to the degree \( 10^\circ \), if it be sufficiently copious in extent. If we do the same thing when the wire which connects the lying plate with the ground is taken away, we know that the same diminution of the electricity of the other plate cannot be produced by bringing it down near the lying insulated plate.

The theory of Volta's condenser now becomes very simple. M. Volta seems to have obscured his conceptions of it, by being intent on the electrophorus which he had lately invented, and was thus led into fruitless attempts to explain the advantages of the imperfect conductor above the perfect insulator. But the condensing apparatus is wholly different from an electrophorus; its operations are more analogous to those of a coated plate not charged, and insulated only on one side; and such a coated plate lying on a table will be a complete condenser, if the upper coating be of the same dimensions as the plate of the condenser. All the directions given by M. Volta for preparing the imperfect conductors prove, that the effect produced is to make them as perfect conductors as possible for any degree of electricity that exceeds a certain small intensity, but such as shall not suffer this very weak electricity to clear the first step of the conducting space. The marble must be thoroughly dried, and even heated in an oven, and either used in this warm state, or must be varnished, so as to prevent the reabsorption of moisture. We know that marble of slender dimensions, so as to be completely dried throughout, will not conduct electricity till it has again become moist. A thick piece of marble is rendered dry only superficially, and still conducts internally. It is then in the best possible state for a condenser. The same is the case with dry unbaked wood. Varnishing the upper surface of a piece of marble or wood is equivalent to covering it with a thin glass plate. Now by this method of covering the top of the marble, a book, or even the table, with a piece of clean dry silk, they all become most perfect condensators. This view of the matter has great advantages. We learn from it how to form a condensing apparatus much more simple and at the same time much more efficacious. We require only the simplest moveable plate, which must be covered on the under side with a very thin coating of the finest coach-painters varnish. By connecting this, by a wire, with the substance whose weak electricity is to be examined, this electricity will be raised in the proportion of the thicknesses of the varnish to the fourth of the plate's diameter. This condensation will be produced by detaching the wire from the insulating handle of the condensing plate, and then lifting this from the table on which it was lying. It will then afford sparks, though the original electricity Electroelectricity was not strong enough to affect the most delicate electrometer.

**ELECTROPHORUS.** See Electricity Index.

**ELECTRUM,** in Natural History. See Amber.

**ELECTUARY,** in Pharmacy, a form of medicine composed of powders and other ingredients, incorporated with some conserve, honey, or syrup; to be divided into doses, like boluses, when taken.

Vossius observes, that all the remedies prescribed for the sick, as well as the confections taken by way of regale, were called by the Greeks ἐλεκτορία, and ἐλεκτορικός, "I like;" whence, says he, was formed the Latin electarium, and afterwards electuarium. This conjecture he supports from the laws of Sicily, where it is ordained, that electuaries, syrups, and other remedies, be prepared after the legal manner. The Boilandiits, who relate this etymology, seem to confirm it. For the composition and different sorts of electuaries, See Pharmacy.

**ELEEMOSYNA Carucarum,** or pro Aratriis, or Aratrii, in our ancient customs, a penny which King Ethelred ordered to be paid for every plough in England towards the support of the poor. Sometimes it is also called eleemosyna regis, because first appointed by the king.

**ELEEMOSYNARIUS,** in our old writers, is used for the almoner or peculiar officer who received the eleemosynary rents and gifts, and distributed them to pious and charitable uses. There was such an officer in all religious houses. The bishops also used to have their almoners, as now the king has.

**ELEGANCE,** (from eligo "I choose,") denotes a manner of doing or saying things politely, agreeably, and with choice. With choice, so as to rise above the common manners; politely, so as to strike people of delicate taste; and agreeably, so as to diffuse a relish which gratifies every body.

**ELEGANCE,** in oratory and composition, an ornament of politeness and agreeableness shown in any discourse, with such a choice of rich and happy expressions, as to rise politely above the common manners, so as to strike people of a delicate taste.

It is observed, that elegance, though irregular, is preferable to regularity without elegance: that is, by being so scrupulous of grammatical construction, we lose certain licences wherein the elegance of language consists.

**ELEGIA,** in ancient poetry, anything belonging to elegy. See Elegy.

**ELEGIT,** in Law, a writ of execution, which lies for a person who has recovered debt or damages; or upon a recognition in any court, against a defendant that is not able to satisfy the same in his goods.

**ELEGY,** a mournful and plaintive kind of poem. See the article Poetry.

**ELEMENTS,** in Physics, the first principles of which all bodies in the system of nature are composed.

These are supposed to be few in number, unchangeable, and by their combinations to produce that extensive variety of objects to be met with in the works of nature.

That there is in reality some foundation for this doctrine of elementary bodies is plain; for there are some principles evidently exempted from every change or decay, and which can be mixed or changed into different elements, forms of matter. A person who surveys the works of nature in an attentive manner, may perhaps form a contrary opinion, when he considers the numerous tribes of fossils, plants, and animals, with the wonderful variety that appears among them in almost every instance. He may from thence be induced to conclude, that nature employs a vast variety of materials in producing such prodigious diversity. But let him inquire into the origin of this apparent diversity, and he will find that these bodies which seem the most different from each other are composed nearly of the same elements. Thus the blood, chyle, milk, urine, &c., as well as the various solid parts of animals, are all composed of one particular substance; galls, for instance, by the affluence of air and water, and even sometimes of very insipid kinds of galls. The same simplicity prevails itself in the original composition of the nourishment of vegetables, notwithstanding the variety among them with respect to hardness, loftiness, elasticity, taste, odour, and medical qualities. They chiefly depend, for these, upon water and the light of the sun; and the same simplicity must take place in animals that are fed on vegetables. The analysis of animal substances confirms this hypothesis; for they can all be reduced into a few principles, which are the same in all, and only differ with regard to the proportions in which they are combined. With regard to animals, the case appears to be the same: and the more we are acquainted with them, the more reason we have to believe that the variety in their origin is very small.

Notwithstanding the infinite variety of natural productions, therefore, it appears, that the materials employed in their formation are but few; that these are uniformly and certainly the same, totally exempted from any change or decay; and that the constant and gradual change of one body into another is produced by the various separations and combinations of the original and elementary parts, which is plain from the regularity and uniformity of nature at all times. There is a change of forms and combinations through which it passes, and this has been the case from the earliest accounts of time; the productions of nature have always been of the same kind, and succeeded one another in the same order. If we examine an oak, for instance, we find it composed of the same matter with that of any other that has existed from the earliest ages. This regularity and uniformity in the course of nature shows that the elementary parts of bodies are permanent and unchangeable; for if these elementary particles which constituted an oak some thousand years ago, had been undergoing any gradual decay, the oaks of the present times would have been found considerably different from those that existed long ago; but as no difference has been observed, it would seem that the ultimate elements of bodies have always continued the same.

Reflections of this kind have suggested an idea of several principal elements of which all other bodies are composed, which by their various combinations furnished all the variety of natural bodies. Democritus, and other great philosophers of antiquity, fixed the number to four, which have retained the name of elements ever since. These are, fire, air, earth, and water; each of which they imagined was naturally disposed. Elements, disposed to hold its own place in the universe. Thus, the earth, as heaviest, naturally tended towards the centre, and occupied the lower parts; the water, as approaching next to it in gravity, was spread chiefly on the outside of the earth; the air, being more subtle and rare, occupied the middle place; while the fire, being still more subtle and active, receded to the greatest distance of all, and was supposed to compose the planets and stars. This system was extended to all the productions of nature. Meteors were produced from a combination of fire and air; animals were considered as composed of earth and water; and those that were warm had likewise a proportion of the element of fire. Thus they went on, explaining some of the most striking qualities of the several productions of nature from the different proportions of the four elements they contained.

But though this system appears not at all defective in beauty and propriety, and on this account has been long received, we know from modern discoveries that these four substances are not really elementary bodies; nor do they answer our purpose in forming a system, as we know too little of the intimate structure and texture of them to enable us to explain other bodies by them.

Any other attempts that have been made to assign the number of elementary bodies have been much less fortunate. The older chemists, with Paracelsus at their head, pretend to speak of four elementary bodies, salt, sulphur, earth, and mercury: but when we attempt to form an idea of what they mean, we find it very perplexed; and that the expressions concerning them are enveloped in so much obscurity, that they cannot be comprehended; and the theory is built entirely upon experiments made on metallic substances.

Attempts have been made by some to show that the elements, whatever they are, must necessarily be invisible or imperceptible by any of our senses. An inquiry into their number or properties therefore must be attended with very little success; and all the knowledge we can have upon the subject must be drawn from a view of their combinations, and reasoning analogically from the transmutations we observe to take place in nature. The modern discoveries in aerology have enabled us to proceed farther in this way than what it was possible for the ancient philosophers to do. We now find that all the different kinds of air are composed of that invisible and subtle fluid named heat, united in a certain way with some other substance: by which union the compound acquires the properties of gravitation, expansion, rarefaction, &c., for pure heat, unless when united with some terrestrial substance, neither gravitates nor expands. This is evident from the phenomena of the burning glass, where the light concentrated in the focus will neither heat the air nor water, unless it meets with something with which it can form a permanent union. Heat therefore is justly to be considered as one of the original elements; being always capable of uniting with bodies, and of being extricated from them unchanged; while the same bodies are by their union with it changed into various forms; water, for instance, into ice or vapour, both of which return into their original state by the abstraction or addition of heat in a certain degree. Hence it becomes almost natural to conclude, that there are only two elements in the universe; and this opinion we find adopted by several philosophers, particularly the count de Tresilian in his Essay on the Electric Fluid. According to this doctrine, two primitive material substances seem to exist in nature; one that incessantly acts, and to which it is essential to be in motion; the other absolutely passive, and whose nature it is to be inert, and move entirely as directed by the former. Should this doctrine be adopted, little difficulty would occur in determining the active matter to be that universal fluid which in its various modifications of light, heat, and electricity, has such a share in the operations of nature. But in fixing on the passive element we are greatly embarrassed; nor are the discoveries in aerology or any other science as yet able to remove the difficulty entirely. According to the doctrines which long prevailed among chemical philosophers, there are three things that seem to be unchangeable, viz. earth; phlogiston; and that invisible, though terrestrial and gravitating principle, called by the antiphlogitians the oxygenous or acidifying principle, and by the phlogitians the basis of dephlogisticated air. In our experiments, say they, on the first, we find that earth, though vitrified by the most intense fire, may be recovered in its proper form; and some very pure earths, particularly magnesia alba, cannot be changed even in the focus of the most powerful mirror. In like manner we may dilute charcoal in vacuo by the solar rays, and the compound is inflammable air: we may decompose this compound by a metallic calx, and we have our charcoal again unchanged, for all metals contain charcoal in substance. Let us try to destroy it by common fire, and we have it then in the fixed air produced, from which it may be recovered unchanged by means of the electric spark. With the basis of dephlogisticated air the case is still more difficult; for we cannot by any means procure a sight of it by itself. We may combine it with heat, and we have dephlogisticated air; to the compound we may add charcoal, and we have fixed air: by decomposing the former by burning iron in it, we have the metal greatly increased in weight by some unknown substance: and if we attempt to separate the latter, we have water, or some kind of vapour which still conceals it from our view.

In some experiments which were made by the ingenious Mr Watt, it was found that nitrous acid might be phlogisticated by the purest earth or metallic calx; whence, according to this doctrine, it is not unreasonable to suppose that phlogiston may be only a certain modification of earth, and not an element distinct from it: but with regard to the basis of dephlogisticated air, no experiment has ever shown that it can either be procured by itself, or changed into any other substance; so that it appears to have the nature of an element as much as light or heat. Though we should therefore be inclined to divide the whole matter of the universe into two classes, the one active and the other acted upon, we must allow that the passive matter even on this earth is not precisely of the same kind: much less are we to extend our speculations in this respect to the celestial regions; for who can determine whether the substance of the moon is the same with that of our earth, or that the elements of Jupiter are the same with those of Saturn? There is even a difficulty with regard to the division which seems so well established, viz., of matter in general into active Element active and passive; for no person can prove, that the matter which is active in one case may not be passive in another, and occasionally resume its activity. Something like this certainly happens in the case of the electric fluid, which is modified into heat or light, according to different circumstances; and we cannot know but it is the very same substance that constitutes the most solid bodies. This opinion at least did not seem absurd to Sir Isaac Newton, who proposed it as a query, Whether gross bodies and light were not convertible into one another? The end of our inquiries on this subject therefore must be, That the universe may be composed of many elements, or of one element; and of the nature of these elements, or of the single one, we know nothing.