him a little below his hips. To the iron rings of the girdle a rope was fixed; the rope went between his legs, and through a flit of the prop. Several men, or even two horfes, could not by pulling move him out of his place: he feerned to pull with his hands, but thefe were of no advantage to him.

The fame man having fixed a rope to a ftrong poft, paffed it through a fixed iron eye, then hooked it on his girdle, and fetting his feet against the poft, near the faid eye, raifed himfelf from the ground by the rope; which he broke by fuddenly ftretching out his legs, and fell backwards on a featherbed, laid on the ground to catch him.

He lay down on the ground, with an anvil on his breaft, upon which another man hammered with all his force a piece of iron with a fledgehammer.

He put his fhoulders upon one chair, and his heels upon another, and fupported one or two men ftanding upon his belly, railing them up and down as he breathed; making with his back-bone, thighs, and legs, an arch; the abutment being on the chairs.

He lay down on the ground, a man standing upon his knees; he then drew his heels towards his breech, and fo raifed his knecs till they were perpendicular under the man; when he raifed up his own body, and putting his arms about the man's legs, rifes with him, and fets him down on a low table. This he fometimes did with two men.

OF WHEEL CARRIAGES.

By what we have feen of man, confidered as a machine, it is easy to observe that his frame is not adapted to drawing carriages; while, on the con

trary

trary, in that of an animal upon all fours, the column of whofe bodies, and the fituation of whofe muscles, act almoft directly upon bodies placed behind them, they are perfectly fitted by nature for this kind of fervice. Horfes are ufually employed in the draft in England; mules, oxen, and other animals, are fometimes used in other parts of the world. It might incur ridicule, if we pretended to inform the learner, that each of thefe will draw a weight or carriage in proportion as they are ftrong: but notwithstanding this is generally the cafe, yet we are going to mention what will feem a paradox; namely, that two horfes may be found, one stronger than the other, and alfo better skilled in the draft, yet the weaker shall draw a weight, with the very fame carriage, the ftronger one could not remove! This will be effected if the weakeft horse be the heavieft; if he exceeds his antagonist morc in weight than he is exceeded in strength. I have before obferved, that the weight re-acts and pulls back the horse, as much as the horse acts upon the weight to pull it forward. Now the horfe has two fources of power in drawing the weight along; his ftrength, which gives him velocity, and his weight, which, added, gives force; and it is evident, that the horfe which hath both in the greatest proportion will draw the heaviest weights. If we fhould imagine both horfes raifing an equal weight from a deep pit, and this weight ftill increafed, fo as to overcome their strength, it is plain that the lighteft horse would fooneft be drawn in. We have feveral instances, in ordinary, practice, of the great benefit of increasing the horfe's weight to promote his draft.

Horfes have little or no power to draw, but what they have from gravity, or weight; otherwife

VOL. III.

A a

they

they could take no hold of the ground, and then they muft flip, and draw nothing.

Common experience will inform you, that if a horfe is to convey a certain weight, he ought (that he may draw the better) have a proportionable weight on his back or fhoulders. A horfe in a two-wheeled cart, in which there is a ton weight, when it is in an equilibrium will not be able to draw it; but when there are fifty or fixty pounds bearing on his back, he will draw it with eafe. If it be two or three ton, if he bears one hundred or two hundred pounds on his back, he will be able to draw the load, becaufe the wheels of a cart are very high.

When a horse draws hard, he bends forward, and brings his breaft nearer the ground; and then, if the wheels are very high, he is pulling the carriage against the ground.

A horfe tackled in a waggon will draw two or three tons weight, because the line of traction is below his breaft.

It is very common, when one horfe is drawing a heavy load, to fee his fore-fect rife from the ground, and he will nearly ftand an end. It is ufual in this cafe to add a weight on his back, to keep his fore-feet down, by a perfon mounting on him, which will enable him to draw the load he could not move before.

The cafe is nearly the fame in applying the frength of a man in wheeling a load in a wheelbarrow. When most of the load lies on the wheel, he will flip, and not be able to get it forward; but then bring the weight nearer his arms, he will be able to drive it forward. In drawing a heavy garden-roll, if the axis of motion were even with that part of his body where his arms are extended, he could not be able to draw it along; but will draw it afily, it the line of traction is low.

In a loaded cart which hangs nearly in equilibrio, if two men were to take it by the fhafts, then they would not be able to move it; but one of them in the fhafts and the other behind the cart, pushing the breech upward as well as forward, he lays a load on the first man's back, and fo preffing both the feet against the ground they will eafily draw the load.

In a long team where only the hind horse bears on his back, if you take off half the number and fix them to a lower point of traction, they will be able to move a much greater weight.

Sledges were probably the firft machines ufed in carrying loads; we find them thus employed in Homer, in conveying wood for the funeral pile of Patroclus. There are fome countries alfo, that preferve their ufe to this day. However, men early. began to find how much more eafily a machine could be drawn upon a rough road, that run upon wheels, than one that thus went with a fliding motion. And indeed, if all furfaces were smooth and even, bodies could be drawn with as much ease upon a fledge as upon wheels; and in Holland, Lapland, and other countries, they ufe fledges upon the fmooth furface of the ice; for as every furface upon which we travel is ufually rough, wheels have been made ufe of, which rub lefs against the inequalities than fledges would do. In fact, wheels would not turn at all upon ice, if it were perfectly fmooth, for the caufe of the wheels turning upon a common road, is the obftacles it continually meets. For if we fuppofe the wheels to be lifted from the ground, and carried along in the air, the wheels in zhis cafe would not turn at all, for there would be nothing to put any part into motion rather than another; in the fame manner, if they were carried along upon perfectly fmooth ice, they would meet nothing to give a beginning to the circulatory mozion, and all their parts would reft equally alike. A a 2

But

But if we fuppofe the wheel drawn along a commoni road, then the parts will receive unequal óbftructions, for it meets with obftacles that retard it at bottom, therefore the upper part of the wheel, which is not retarded, will move more fwiftly than the lower part, which is; but this it cannot do, unless the wheel moves round. And thus it is, that the obftacles in the rough road cause this circulatory motion in the wheel.

The utility of wheels arifes therefore from their turning about their axis, the refiftance arifing from friction is very much diminished, and the draft is thereby rendered more eafy; and you will find by experiment that it requires confiderably lefs force to draw a carriage when the wheels are free to turn about their axis, than when they are chained together and cannot turn. According to Heltham, a carriage with four wheels will be drawn with five times as fmall an effort as one that flides on the fame furface in a fledge. From the foregoing experiment it not only appears that the friction is very much leffened, but that this diminution does not arise from the wheels touching the plane in a few points, but to their rotation on their axis.

A fledge paffing over a plane undergoes a friction, or rubbing of it's parts against the plane equal to the distance through which it moves; but if an axis be applied whofe circumference is fix inches, and on that a wheel be placed whofe circumference is eighteen feet, it is evident that in moving the carriage eighteen feet over a plane the wheels will make but one revolution; and as there is no fliding of the parts between the plane and the wheels, but only a mere change of furface, by one part of the wheel rifing and the other defcending nearly perpendicular to the plane, no friction will take place there, the whole being transferred to the nave acting on the axis, which nave having

made