iron united with carbons. See IRON.

Steel has properties distinct from those of iron, which render it of superior value. From its higher degree of hardness it admits a finer polish and assumes a brighter colour. When tempered, it possesses a higher degree of elasticity, and is also more sonorous. It is more weakly attracted by the lodestone, it receives more slowly the magnetic power, but it preserves it longer. When exposed to a moist air, it does not contract rust so easily as iron. iron. It is also heavier, increasing in weight, according to Chaptal, one hundred and seventieth part. M. Rimann has given as the result of several accurate experiments on different kinds of steel the following specific gravity: 7.795; while he makes ductile iron 7.750, and crude iron 7.251.

All iron is convertible into steel by exposing it to a certain degree of heat for a certain time along with a quantity of charcoal. Chemists differ in opinion concerning the nature and effects of this process. Some say that steel is produced by absorbing a quantity of caloric or heat in a latent state, as the older chemists had said it was formed by absorbing phlogiston. Lavoisier seems to have ascribed the qualities of steel to a slight degree of oxidation, others to a combination with plumbago or black lead, and others to a union with carbone. In agreeing with those who say the formation of steel is owing to carbone, we do not differ essentially from those who attribute it to plumbago; for the art of chemistry has now found that these substances are very nearly allied. Plumbago is a true charcoal combined with a little iron. The brilliant charcoal of certain vegetable substances, more especially when formed by distillation in close vessels, possesses all the characters of plumbago. The charcoal of animal substances possesses characters still more peculiarly resembling it. Like it they are difficult to incinerate, they leave the same impression on the hands and upon paper; they likewise contain iron, and become converted into carbonic acid by combustion. When animal substances are distilled by a strong fire, a very fine powder sublimes, which attaches itself to the inner part of the neck of the retort, and this substance may be made into excellent black lead pencils.

There are two ways of making steel, namely, by fusion and by cementation. The first way is used to convert iron into steel immediately from the ore, or from crude or cast-iron. By the second way, bar-iron is exposed to a long continued heat surrounded by charcoal. Each of these ways has advantages peculiar to itself; but the same causes in fact predominate in both, for both kinds of steel are produced by heat and charcoal. The only difference between the two methods is this; in making steel by fusion the charcoal is not so equally defended from the access of air as in the other way.

Swedenborgius has given the following description of the method used in Dalecarlia for making steel from cast-iron. The ore from which the crude iron to be converted into steel is obtained is of a good kind. It is black, friable, and composed of many small grains, and it produces very tough iron. The conversion into steel is made upon a forge-hearth, something smaller than common. The sides and bottom are made of cast-iron. The tuyere is placed, with very little inclination, on one of the side-plates. The breadth of the fire-place is fourteen inches; its length is greater. The lower part of the tuyere is six inches and a half above the bottom. In the interior part of the fire-place there is an oblong opening for the flowing of the superfluous scoriae. The workmen first put scoriae on the bottom, then charcoal and powder of charcoal, and upon these the cast-iron run or cut into small pieces. They cover the iron with more charcoal, and excite the fire. When the pieces of iron are of a red white, and before they begin to melt, they stop the bellows, and carry the mass under a large hammer, where they break it into pieces of three or four pounds each. The pieces are again brought to the hearth, and laid within reach of the workman, who plunges some of them into the fire, and covers them with coal. The bellows are made to blow slowly till the iron is liquefied. Then the fire is increased; and when the fusion has been long enough continued, the scoriae are allowed to flow out; and at that time the iron hardens. The workman adds more of the pieces of crude iron, which he treats in the same manner; and so on a third and a fourth time, till he obtains a mass of steel of about a hundred pounds, which is generally done in about four hours. This mass is raised and carried to the hammer, where it is forged, and cut into four pieces, which are farther beat into square bars four or five feet long. When the steel is thus forged, it is thrown into water that it may be easily broken; for it is yet crude and coarse-grained. The steel is then carried to another hearth similar to the former, and there broken in pieces. These pieces are laid regularly in the fire-place, first two parallel, upon which seven or eight others are placed across; then a third row across the second, in such a manner that there is space left between those of the same row. The whole is then covered with charcoal, and the fire is excited. In about half or three quarters of an hour the pieces are made hot enough, and are then taken from the fire, one by one, to the hammer, to be forged into little bars from half a foot to two feet long, and while hot are thrown into water to be hardened. Of these pieces fifteen or twenty are put together so as to make a bundle, which is heated and welded, and afterwards forged into bars four inches thick, which are then broken into pieces of convenient length for use.

The method of converting iron into steel by cementation is a very simple process. It consists solely in exposing it for a certain time to a strong degree of heat, while closely covered with charcoal and defended from the external air. The furnaces employed for converting iron into steel (says a manufacturer of this metal) are of different sizes; some capable of converting only three or four tons weight, while others are spacious enough to contain from seven to eight or ten tons. The outsides of these furnaces rise up in the form of a cone, or sugar-loaf, to the height of a very considerable number of feet. In the inside, opposite to each other, are placed two very long chests, made either of stone, or of bricks capable of bearing the strongest fire; which is placed between the two chests. The bars of iron, after the bottom is furnished with a necessary quantity of charcoal dust, are laid in stratum super stratum, with intermediate beds of the charcoal dust, to such a height of the chests as only to admit of a good bed at top; which is then all covered over, to prevent the admission of the common air; which, could it procure an entrance, would greatly injure the operation. The iron being thus situated, the fire is lighted; which is some time before it can be raised to a sufficient degree of heat to produce any considerable effect. After which it is continued for so many days as the operator may judge proper; only now and then drawing out what they call a proof bar. This is done by openings fit for the purpose at the ends of the chest, which are easily and with expedition stopped up again, without occasioning any injury to the contents left behind. When the opera- tor apprehends the conversion is sufficiently completed, the fire is suffered to go out, and the furnace, with its contents, is left gradually to cool. This may take up several days; after which the furnace is discharged, by taking out the bars of steel and the remainder of the charcoal dust.

There is a manufactory established in the parish of Cramond, about five miles from Edinburgh, in which this method is practised with great success. Great quantities of steel are made there, which we have reason to believe is of as excellent a quality as any that can be procured from other countries.

When the charcoal is taken out, it is found as black as before it was introduced into the furnace, unless by accident the external air has got admittance. The bars preserve their exterior form only; the surface frequently exhibits a great number of tumors or blisters, whence they are called blistered steel.

The hardness of steel is much increased by tempering. This consists in heating it to a red heat, and then plunging it suddenly into cold water. If it be allowed to cool slowly, it still preserves its ductility; or if it be heated again after being tempered, it loses its hardness, and again becomes ductile. In heating steel for tempering it, the most remarkable circumstance is, the different colours it assumes, according to the degree of heat it has received. As it is gradually heated, it becomes white, then yellow, orange, purple, violet, and at last of a deep blue colour.

According to Reaumur, the steel which is most heated in tempering is generally the hardest. Hence it is believed, that the more violent the heat to which steel is exposed, and the more suddenly it is plunged into cold water, the harder the steel will be. Rinman, again, has deduced a conclusion directly opposite, that the steel which is naturally hardest demands the least degree of heat to temper it. Different methods have been proposed to determine what degree of heat is most proper; but the easiest method is to take a bar of steel, to long, that while one end is exposed to a violent heat, the other may be kept cold. By examining the intermediate portions, it may be found what degree of heat has produced the greatest hardness.

By tempering, steel is said to increase both in bulk and in weight. Reaumur says, that a small bar six inches long, six lines broad, and half an inch thick, was increased at least a line in length after being tempered to a reddish white colour; that is, supposing the dilatation proportional in all dimensions increasing at the rate of 48 to 49. Iron also expands when heated; but when the heat palls off, it returns to its former dimensions. That the weight of steel is also augmented by tempering, has been found by experiment. Rinman having weighed exactly in an hydrostatic balance two kinds of fine steel made by cementation, and not tempered, found their density to be to that of water as 7,991 to 1; after being tempered, the density of the one was 7,553, and that of the other 7,708. M. de Morveau took three bars just of a size to enter a certain caliber 28 lines long, and each side two lines broad; one of the bars was soft iron, and the two others were taken from the same piece of fine steel. In order to communicate an equal degree of heat to each, in an earthen vessel in the midst of a wind furnace, the bar of soft iron and one of the bars of steel were thrown into cold water; the other bar of steel was cooled slowly over some pieces of charcoal at a distance from the furnace. The bar of iron and the one of steel that was allowed to cool slowly passed easily into the caliber again; but the bar of tempered steel was lengthened almost one-ninth of a line.

There is no doubt but tempering changes the grain; that is, the appearance of the texture of a piece of steel when broken. This is the mark which is usually observed in judging of the quality of steel, or of the tempering which suits it best. The tempered bar is broken in several places after having received different degrees of heat in different places. What proves completely the effect of heat upon the grain, at least in some kinds of steel, is, that a bar of steel exposed to all the intermediate degrees of heat, from the finest sensible heat to a red heat, is found to increase in fineness of grain from the slightly heated to the strongly heated end. The celebrated Rinman has made many experiments on the qualities of steel exposed to different degrees of heat in tempering, but particularly to three kinds, viz. steel heated to an obscure red, to a bright red, and to a red white. Hard brittle steel, made by cementation, and heated to an obscure red and tempered, exhibited a fine grain, somewhat shining, and was of a yellow white colour. When tempered at a bright red heat, the grain was coarser and more shining; when tempered at a red white heat, the grain was also coarse and shining.

With a view to determine how far steel might be improved in its grain by tempering it in different ways, M. de Morveau took a bar of blistered steel, and broke it into four parts nearly of the same weight. They were all heated to a red heat in the same furnace, and withdrawn from the fire at the same instant. One of the pieces was left at the side of the furnace to cool in the air, the second was plunged into cold water, the third into oil, and the fourth into mercury. The piece of steel that was cooled in the air resisted the hammer a long time before it was broken; it was necessary to notch it by the file, and even then it was broken with difficulty. It showed in its fracture a grain sensibly more fine and more shining than it was before. The second piece, which had been plunged into water, broke easily; its grain was rather finer than the first, and almost of the same white colour. The third piece, which was tempered in oil, appeared very hard when tried by the file; it was scarcely possible to break it. Its grain was as fine, but not quite so bright, as that which was tempered in water. The fourth piece, which was dipped into mercury, was evidently superior to all the rest in the fineness and colour of the grain. It broke into many fragments with the first stroke of the hammer, the fractures being generally transverse.

M. de Morveau was not altogether satisfied with these experiments, and therefore thought it necessary to repeat them with finer steel. He took a bar of steel two lines square, such as is used in Germany for tools by engravers and watchmakers; he divided it into four pieces, and treated them in the same way as he had done the blistered steel. The first piece, which was cooled in the air, it was very difficult to break: the fracture appeared in the midst of the grain very fine, but white and shining. The second, which was tempered in water, was broken into three fragments at the first blow; its grain was perfectly equal, of a grey ash- colour, and of remarkable fineness. One of its sides was polished, and a drop of the nitrous acid which was pour- ed upon it left a black spot, but not deep. But when a drop of the same acid was poured on the middle of the fracture, after it had been equally polished, it left a black spot much deeper. The third piece, which was plum- bed in oil, bent as easily as the piece which was cooled in the air; the file made an impression on it with diffi- culty; it was necessary to break it with a vice; its grain was inferior in fineness to the second, but it was of a darker colour. The fourth, which was tempered in mercury, exhibited a grain of an intermediate fineness between the second and the third. From these experi- ments, it appears that steel may be hardened by tem- pering it, not only with water, but with any other liquid which is capable of accelerating its cooling.

Steel may be unmade, or reduced to the state of iron, by a management similar to that by which it is made, that is, by cementation. But the cement used for this purpose must be composed of substances en- tirely free from inflammable matter, and rather ca- pable of absorbing it, as calcareous earth or quicklime. By a cementation with calcareous earth, continued during eight or ten hours, steel is reduced to the state of iron. After it has been tempered, it may be again untempered, and softened to any degree that we think proper; for which purpose we have only to heat it more or less, and to let it cool slowly. By this me- thod we may soften the hardest-tempered steel.

STEEL-BOW Tenants. See TENURE.

Salt of STEEL. See CHEMISTRY, p. 697.

STEEL-YARD, is one of the most ancient presents which science has made to society; and though long in defectuosity in this country, is in most nations of the world the only instrument for ascertaining the weight of bodies. What is translated balance in the Penta- teuch, is in fact steelyard, being the word used by the Arabs to this day for their instrument, which is a steel- yard. It is in common use in all the Asiatic nations. It was the flatera of the Greeks and Romans, and seems to have been more confided in by them than the bal- ance; for which reason it was used by the goldsmiths, while the balance was the instrument of the people.— Non aurificis flatera sed populari truina examinare. Cic. de Or. 238.

The steelyard is a lever of unequal arms, and, in its most perfect form, is constructed much like a common balance. It hangs in sheers E (fig. 1.) resting on the nail C, and the scale L for holding the goods hangs by a nail D on the short arm BC. The counter weight P hangs by a ring of tempered steel, made sharp in the inside, that it may bear on an edge on the long arm CA of the steelyard. The under edge of the centre nail C, and the upper edge of the nail D, are in the straight line formed by the upper edge of the long arm. Thus the three points of suspension are in one straight line. The needle or index of the steelyard is perpen- dicular to the line of the arms, and plays between the sheers. The short arm may be made so massive, that, together with the scale, it will balance the long arm un- loaded. When no goods are in the scale, and the coun- ter weight with its hook are removed, the steelyard ac- quires a horizontal position, in consequence of its centre of gravity being below the axis of suspension. The rules for its accurate construction are the same as for a common balance.

The instrument indicates different weights in the fol- lowing manner: The distance CD of the two nails is considered as an unit, and the long arm is divided into a number of parts equal to it; and these are subdivided as low as is thought proper: or in general, the long arm is made a scale of equal parts, commencing at the edge of the nail C; and the short arm contains some de- termined number of those equal parts. Suppose, then, that a weight A of 10 pounds is put into the scale L. The counterpoise P must be of such a weight, that, when hanging at the division 10, it shall balance this weight A. Now let any unknown weight W be put into the scale. Slide the hook of the counterpoise along the long arm till it balances this weight. Suppose it then hanging at the division 38. We conclude that there is 38 pounds in the scale. This we do on the authority of the fundamental property of the lever, that forces acting on it, and balancing each other, are in the inverse proportion of the distances from the ful- crum to their lines of direction. Whatever weight the counterpoise is, it is to A as CD to 10, and it is to the weight W as CD to 38; therefore A is to the weight W as 10 to 38, and W is 38 pounds: and thus the weight in the scale will always be indicated by the division at which it is balanced by the counter- poise.

Our well informed readers know that this fundamen- tal property of the lever was discovered by the renown- ed Archimedes, or at least first demonstrated by him; and that his demonstration, besides the defect of being applicable only to commensurable lengths of the arms, has been thought by metaphysicians of the first note to proceed on a postulate which seems equally to need a demonstration. It has accordingly employed the ut- most refinement of the first mathematicians of Europe to furnish a demonstration free from objection. Mr. D'Alembert has given two, remarkable for their inge- nuity and subtlety; Foncenex has done the same; and Professor Hamilton of Trinity college, Dublin, has giv- en one which is thought the least exceptionable. But critics have even objected to this, as depending on a postulate which should have been demonstrated.

Since we published the volume containing the article MECHANICS, there has appeared (Phil. Trans. 1794) a demonstration by Mr Vince, which we think unexcep- tionable, and of such simplicity that it is astonishing that it has not occurred to any person who thinks on the subject. Our readers will not be displeased with an account of it.

Let AE (fig. 2.) be a mathematical lever, or in- flexible straight line, resting on the prop A, and sup- ported at E by a force acting upwards. Let two equal weights b and d be hung on at B and D, equidistant from A and E. Pressures are now exerted at A and E; and because every circumstance of weight and dis- tance is the same, the pressure at E, arising from the action of the weight b on the point B, must be the same with the pressure at A, arising from the action of the weight d on the point D; and the pressure at E, occa- sioned by the weight d, must be the same with the pressure at A, occasioned by the weight b. This must be the case wherever the weights are hung, provided that the distance AB and DE are equal. Moreover, Steel-yard. The sum of the pressures at A and E is unquestionably equal to the sum of the weights, because the weights are supported solely at A and E. Let the two weights be hung on at C the middle point; the pressure at E is still the same. Therefore, in general, the pressure excited at the point E, by two equal weights hanging at any points B and D, is the same as if they were hung on at the middle point between them: but the pressure excited at E is a just measure of the effort or energy of the weights b and d to urge the lever round the point A. It is, at least, a measure of the opposite force which must be applied at E to sustain or balance this pressure. A very fatidious metaphysician may still say, that the demonstration is limited to a point E, whose distance from A is twice AC, or \(= AB + AD\). But it extends to any other point, on the authority of a postulate which cannot be refused, viz. that in whatever proportion the pressure at E is augmented or diminished, the pressure at this other point must augment or diminish in the same proportion. This being proved, the general theorem may be demonstrated in all proportions of distance, in the manner of Archimedes, at once the most simple, perspicuous, and elegant of all.

We cannot help observing, that all this difficulty (and it is a real one to the philosopher who aims at rendering mechanics a demonstrative science) has arisen from an improper search after simplicity. Had Archimedes taken a lever as it really exists in nature, and considered it as material, consisting of atoms united by cohesion; and had he traced the intermediate pressures by whose means the two external weights are put in opposition to each other, or rather to the support given to the fulcrum; all difficulty would have vanished. (See what is said on this subject in the article Strength of Timber, &c.)

The quantity of goods which may be weighed by this instrument depends on the weight of the counterpoise, and on the distance CD from the fulcrum at which the goods are suspended. A double counterpoise hanging at the same division will balance or indicate a double quantity of goods hanging at D; and any counterpoise will balance and indicate a double quantity of goods, if the distance CD be reduced to one-half. Many steelyards have two or more points of suspension D, to which the scale may occasionally be attached. Fig. 6. of Plate XCI Vol. II. represents one of these. It is evident, that in this case the value or indication of the divisions of the long arm will be different, according to the point from which the scale is suspended. The same division which would indicate 20 pounds when CD is three inches, will indicate 30 pounds when it is two inches. As it would expose to chance of mistakes, and be otherwise troublesome to make this reduction, it is usual to make as many divided scales on the long arm as there are points of suspension D on the short arm; and each scale having its own numbers, all trouble and all chance of mistake is avoided.

But the range of this instrument is not altogether at the pleasure of the maker. Besides the inability of a slender beam to carry a great load, the divisions of the scale answering to pounds or half-pounds become very minute when the distance CD is very short; and the balance becomes less delicate, that is, less sensibly affected by small differences of weight. This is because in such cases the thickness which it is necessary to give the edges of the nails does then bear a sensible proportion to the distance CD between them; so that when the balance inclines to one side, that arm is sensibly shortened, and therefore the energy of the preponderating weight is lessened.

We have hitherto supposed the steelyard to be in equilibrium when not loaded. But this is not necessary, nor is it usual in those which are commonly made. The long arm commonly preponderates considerably. This makes no difference, except in the beginning of the scale. The preponderancy of the long arm is equivalent to some goods already in the scale, suppose four pounds. Therefore when there are really 10 pounds in the scale, the counterpoise will balance it when hanging at the division 6. This division is therefore reckoned 10, and the rest of the divisions are numbered accordingly.

A scientific examination of the steelyard will convince us that it is inferior to the balance of equal arms in point of sensibility: But it is extremely compendious and convenient; and when accurately made and attentively used, it is abundantly exact for most commercial purposes. We have seen one at Leipzig which has been in use since the year 1718, which is very sensible to a difference of one pound, when loaded with nearly three tons on the short arm; and we saw a waggon loaded with more than two tons weighed by it in about five minutes.

The steelyard in common use in the different countries of Europe is of a construction still simpler than what we have described. It consists of a batten of hard wood, having a heavy lump A (fig. 3.) at one end, and a swivel-hook B at the other. The goods to be weighed are suspended on the hook, and the whole is carried in a loop of whip-cord C, in which it is slid backward and forward, till the goods are balanced by the weight of the other end. The weight of the goods is estimated by the place of the loop on a scale of divisions in harmonic progression. They are marked (we presume) by trial with known weights.

The chief use that is now made of the steelyard in these kingdoms is for the weighing of loaded waggons and carts. For this it is extremely convenient, and more than sufficiently exact for the purpose in view. We shall describe one or two of the most remarkable; and we shall begin with that at Leipzig already mentioned.

This steelyard is represented in fig. 4. as run out, and just about to be hooked for lifting up the load. The steelyard itself is OPQ, and is about 12 feet long. The short arm PQ has two points of suspension c and d; and the stirrup which carries the chains for holding the load is made with a double hook, instead of a double eye, that it may be easily removed from the one pin to the other. For this purpose the two hooks are connected above by an haft or staple, which goes over the arm of the steelyard like an arch. This is represented in the little figure above the steelyard. The suspension is shifted when the steelyard is run in under cover, by hooking to this staple the running block of a small tackle which hangs in the door through which the steelyard is run out and in. This operation is easy, but... Steel yard, but necessary, because the stirrup, chains, and the stage on which the load is placed, weigh some hundreds.

The outer pin \( b \) is 14 inches, and the inner one \( c \) is seven inches, distant from the great nail which rests in the sheers. The other arm is about 10 feet long, formed with an obtuse edge above. On the inclined plane on each side of the ridge is drawn the scale of weights adapted to the inner pin \( c \). The scales corresponding to the outer pin \( b \) are drawn on the upright sides. The counterpoise slides along this arm, hanging from a saddle-piece made of brass, that it may not contract rust. The motion is made easy by means of rollers. This is necessary, because the counterpoise is greatly above a hundred weight. This saddle piece has like two laps on each side, on which are engraved vernier scales, which divide their respective scales on the arm into quarters of a pound. Above the saddle is an arch, from the summit of which hangs a little plummet, which shows the equilibrium of the steelyard to the weigher, because the sheers are four feet out of the house, and he cannot see their coincidence with the needle of the steelyard. Lastly, near the end of the long arm are two pins \( d \) and \( e \), for suspending occasionally two eke weights for continuing the scale. These are kept hanging on adjoining hooks, ready to be lifted on by a little tackle, which is also hooked immediately above the pins \( d \) and \( e \).

The scales of weights are laid down on the arm as follows. Let the eke-weights appropriated to the pins \( d \) and \( e \) be called \( D \) and \( E \), and call the counterpoise \( C \). Although the stirrup with its chains and stage weigh some hundreds, yet the length and size of the arm \( OP \) gives it a preponderancy of 300 pounds. Here, then, the scale of weights must commence. The counterpoise weighs about 125 pounds. Therefore,

1. When the load hangs by the pin \( b \), 14 inches from the centre, the distance from one hundred to another on the scale is about 11 inches, and the first scale (on the side of the arm) reaches from 300 to 1200. In order to repeat or continue this, the eke-weight \( E \) is hung on the pin \( e \), and the counterpoise \( C \) is brought back to the mark 300; and the two together balance 1100 pounds hanging at \( b \). Therefore a second scale is begun on the side of the arm, and continued as far out as the first, and therefore its extremity marks 2000; that is, the counterpoise \( C \) at 2000 and the eke-weight \( E \) at \( e \) balance 2000 hanging at \( b \).

2. To continue the scale beyond 2000, the load must be hung on the inner pin \( c \). The eke-weight \( E \) is taken off, and the eke-weight \( D \) is hung on its pin \( d \). The general counterpoise being now brought close to the sheers, it, together with the weight \( D \) at \( d \), balance 2000 pounds hanging at \( c \). A scale is therefore begun on one of the inclined planes a-top, and continued out to 4000, which falls very near to the pin \( d \), each hundred pounds occupying about five inches on the arm. To complete the scale, hang on the eke-weight \( E \) on its pin \( e \), and bring back the counterpoise to the sheers, and the three together balance 3800 hanging at \( c \). Therefore when the counterpoise is now slid out to 4000, it must complete the balance with 5800 hanging at \( c \).

It required a little consideration to find out what proportion of the three weights \( C \), \( D \), and \( E \), would make the repetitions of the scale extend as far as possible, having very little of it expressed twice, or upon two scales, as is the case here. We see that the space corresponding to a single pound is a very sensible quantity on both scales, being one-ninth of an inch on the first two scales, and one-twentieth on the last two.

This very ponderous machine, with its heavy weights, cannot be easily managed without some assistance from mechanics. It is extremely proper to have it susceptible of motion out and in, that it may be protected from the weather, which would soon destroy it by rust. The contrivance here is very effectual, and abundantly simple.

When the steelyard is not in use, it is supported at one end by the iron-rod \( F \), into which the upper end of the sheers is hooked. The upper end of this rod has a strong hook \( E \), and a little below at \( a \) it is pierced with a hole, in which is a very strong bolt or pin of tempered steel, having a roller on each end close to the rod on each side. These rollers rest on two joists, one of which is represented by \( MN \), which traverse the building, with just room enough between them to allow the rod \( F \) to hang freely down. The other end \( O \) of the steelyard rests in the bight of a large flat hook at the end of a chain \( W \), which hangs down between the joists, and is supported on them by a frame with rollers \( H \). This is connected with the rollers at \( G \), which carry the sheers by means of two iron-rods, of which only one can be seen. These connect the two sets of rollers in such a manner that they must always move together, and keep their distance invariable. This motion is produced by means of an endless rope \( HI \) \( ZLKVH \) passing over the pulleys \( I \) and \( K \), which turn between the joists, and hanging down in a bight between them. It is evident that by pulling on the part \( LZ \) we pull the frame of rollers in the direction \( GH \), and thus bring the whole into the position marked by the dotted figure. It is also plain, that by pulling on the part \( LK \) we force the roller frame and the whole apparatus out again.

It remains to show how the load is raised from the ground and weighed. When the steelyard is run out for use, the upper hook \( E \) just enters into the ring \( D \), which hangs from the end of the great oaken lever \( BCA \) about 22 feet long, turning on gudgeons at \( C \) about 5 feet from this end. From the other end \( A \) descends a long iron-rod \( SR \), which has one side formed into a toothed rack that is acted on by a frame of wheel-work turned by an endless screw and winch \( Q \). Therefore when the hook \( E \) is well engaged in the ring \( D \), a man turns the winch, and thus brings down the end \( A \) of the great lever, and raises the load two or three inches from the ground. Everything is now at liberty, and the weigher now manages his weights on the arm of the steelyard till he has made an equilibrium.

We need not describe the operation of letting down the load, disengaging the steelyard from the great lever, and bringing it again under cover. The whole of this service is performed by two men, and may be done in succession by one, and is over in five or six minutes.

The most compendious and economical machine of this kind that we have seen is one, first used (we have heard) for weighing the riders of race-horses, and afterwards STE

Fig. 5. is a plan of the machine. KLMN is the plan of a rectangular box, which has a platform lid or cover, of size sufficient for placing the wheels of a cart or wagon. The box is about a foot deep, and is sunk into the ground till the platform cover is even with the surface. In the middle of the box is an iron lever supported on the fulcrum pin i k, formed like the nail of balance, which rests with its edge on arches of hardened steel firmly fastened to the bottom of the box. This lever goes through one side of the box, and is furnished at its extremity with a hard steel pin l m, also formed to an edge below. In the very middle of the box it is crossed by a third nail of hardened steel g h, also formed to an edge, but on the upper side. These three edges are in one horizontal plane, as in a well made balance.

In the four corners A, A', E', E, of the box are firmly fixed four blocks of tempered steel, having their upper surfaces formed into spherical cavities, well polished and hard tempered. ABCDE represents the upper edge of an iron bar of considerable strength, which rests on the cavities of the steel blocks in A and E, by means of two hard steel studs projecting from its under edge, and formed into obtuse angled points or cones. These points are in a straight line parallel to the side KN of the box. The middle part C of this crooked bar is faced with hard tempered steel below, and is there formed into an edge parallel to AE and KN, by which it rests on the upper edge of the steel pin g h which is in the lever. In a line parallel to AE, and on the upper side of the crooked bar ACE, are fixed two studs or points of hardened steel B and D projecting upwards above half an inch. The platform-cover has four short feet like a stool, terminated by hard steel studs, which are shaped into spherical cavities and well polished. With these it rests on the four steel points B, B', D', D. The bar ACE is kned in such a manner vertically, that the points A, B, D, E and the edge C are all in a horizontal plane. These particulars will be better understood by looking at the elevation in fig. 6. What has been said of the bar ACE must be understood as also said of the bar A' C' E'.

Draw through the centre of the box the line a b c perpendicular to the line AE, BD. It is evident that the bar ACE is equivalent to a lever a b c, having the fulcrum or axis AE resting with its extremity C on the pin h g and loaded at b. It is also evident that a C is to a b as the load on this lever to the pressure which it exerts on the pin g h, and that the same proportion subsists between the whole load on the platform and the pressure which it exerts on the pin g h. It will also appear, on an attentive consideration, that this proportion is not easily deranged in whatever manner the load is placed on the platform. If very unequally, the two ends of the pin c b may be unequally pressed, and the lever wrenched and strained a little; but the total pressure is not changed.

If there be now placed a balance or steelyard at the side LK, in such a manner that one end of it may be directly above the pin l m in the end of the lever EOF, they may be connected by a wire or slender rod, and a weight on the other arm of the balance or steelyard may be put in equilibrium with any load that can be laid on the platform. A small counterpoise being first hung on to balance the apparatus when unloaded, any additional weight will measure the load really laid on the platform. If a b be to a c as 1 to 8, and EO to EF also as 1 to 8, and if a common balance be used above, 64 pounds on the platform will be balanced by one pound in the scale, and every pound will be balanced by 1/8th of an ounce. This would be a very convenient partition for most purposes, as it would enable us to use a common balance and common weights to complete the machine: Or it may be made with a balance of unequal arms, or with a steelyard.

Some have thought to improve this instrument by using edges like those of the nails of a balance, instead of points. But unless made with uncommon accuracy, they will render the balance very dull. The small deviation of the two edges A and E, or of B and D, from perfect parallelism to KN, is equivalent to a broad surface equal to the whole deviation. We imagine that, with no extraordinary care, the machine may be made to weigh within 1/32nd of the truth, which is exact enough for any purpose in commerce.

It is necessary that the points be attached to the bars. Some have put the points at A and E in the blocks of steel fastened to the bottom, because the cavity there lodged water or dirt, which soon destroyed the instrument with rust. But this occasions a change of proportion in the first lever by any shifting of the crooked bars; and this will frequently happen when the wheels of a loaded cart are pushed on the platform. The cavity in the steel flange should have a little rim round it, and it should be kept full of oil. In a nice machine a quarter of an inch of quicksilver would effectually prevent all these inconveniences.

The simplest and most economical form of this machine is to have no balance or second steelyard; but to make the first steelyard EOF a lever of the first kind, viz., having the fulcrum between O and F, and allow it to project far beyond the box. The long or outward arm of this lever is then divided into a scale of weights, commencing at the side of the box. A counterpoise must be chosen, such as will, when at the beginning of the scale, balance the smallest load that will probably be examined. It will be convenient to carry on this scale by means of eke-weights hung on at the extremity of the lever, and to use but one moveable weight. By this method the divisions of the scale will have always one value. The best arrangement is as follows: Place the mark O at the beginning of the scale, and let it extend only to 100, if for pounds; or to 112, if for cwt.; or to 10, if for stones; and let the eke-weights be numbered 1, 2, 3, &c. Let the lowest weight be marked on the beam. This is always to be added to the weight shown by the operation. Let the eke-weights stand at the end of the beam, and let the general counterpoise always hang at O. When the cart is put on the platform, the end of the beam tilts up. Hang on the heaviest eke-weight that is not sufficient to press it down. Now complete the balance by sliding out the counterpoise. Suppose the constant load to be 317 lb, and that the counterpoise stands at 86, and that the eke-weight is 9; we have the load = 986 + 312 = 1298 lbs.