Day's

Two men working at a windlass with handles at right angles, can raise 70 pounds more easily than one can raise 30.-Desaguliers...

A man can exert a force of 40 pounds for a whole day, with the assistance of a fly, when the motion is pretty quick, at about four or five feet in 1".--Desaguliers, Lect. iv. But from the annotation it appears to be doubtful whether the force is 40 pounds or 20

For a short time a man may exert a force of 80 pounds with a fly," when the motion is pretty quick."-Desaguliers

A man going up stairs ascends 14 metres in l1'.-Coulomb

A man going up stairs for a day raises 205 chiliogrammes to the height of a chiliometre.-Coulomb

With a spade a man does as much as in ascending stairs. Coulomb

With a winch a man does as much as in ascending stairs. Coulomb ...

A man carrying wood up stairs raises, together with his own weight, 109 chiliogrammes to one chiliometre.Coulomb..

A man weighing 150 pounds, Fr. can ascend by stairs three feet, Fr. in 1" for 15" or 20".-Coulomb

........

For half an hour, 100 pounds, Fr. may be raised one foot, Fr. in 1".-Coulomb

According to Mr. Buchanan's comparison, the force exerted in turning a winch being made equal to the unit, the force in pumping will be

In ringing

In rowing

...

Allowing the accuracy of Euler's formula, confirmed by Schulze, supposing a man's action to be a maximum when he walks 24 miles an hour, we have 74 for his greatest velocity, ,04(74-) for the force exerted with any other velocity, and ,0160(74-v)2 for the action in each case; thus, when the velocity is one mile an hour, the action is When two miles.. When three

When four...

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.............

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And when five

nuance. work.

1,22

2

And the force in a state of rest becomes 24, or about 70 pounds; with a velocity of two miles, 36 pounds; with three, 24 pounds; and with four, 15.

It is obvious that in the extreme cases this formula is inaccurate, but for moderate velocities it is probably a tolerable approximation.

Coulomb makes the maximum of effect when a man, weighing 70 chiliogrammes, carries a weight of 53 up stairs, but this appears to be too great a load; he considers 145 chiliogrammes as the greatest weight that can be raised. He observes that in Martinique, where the thermometer is seldom below 68°, the labour of Europeans is reduced to one half.

Harriot asserts that his pump, with a horizontal motion, enables a man to do one-third more work than the common pump with a vertical motion.

Porters carry from 200 to 300 pounds at the rate of three miles an hour; chairmen walk four miles an hour with a load of 150 pounds each; and it is said that in Turkey there are porters who, by stooping forward, carry from 700 to 900 pounds placed very low on their backs.

The most advantageous weight for a man of common strength to carry horizontally, is 111 pounds; or if he returns unladen, 135. With wheel-barrows, men will do half as much more work as with hods.-Coulomb.

Performance of men by machines.

A man raised by a rope and pulley 25 pounds, Fr. 220 feet, Fr. in 145".-Amontons

A man can raise, by a good common pump, a hogshead of water 10 feet high in a minute, for a whole dayDesaguliers,

By the mercurial pump, or any other good pump, a man may raise a hogshead 18 or 20 feet in a minute, for one or two minutes

In a pile engine, 55 pounds, Fr. were raised one foot, Fr. in 1" for five hours a day, by a rope drawn horizontally.-Coulomb

Robison says, that a feeble old man raised seven cubic feet of water, 114 feet in l', for eight or ten hours a day, by walking backwards and forwards on a lever.-Enc. Br. A young man weighing 135 pounds, and carrying 30, raised 94 cubic feet, 114 feet high, for 10 hours a day, without fatigue.-Robison

Wynner's machine enables a man to raise a hogshead 20 feet in a minute.-Y.......

Force of horses.

Two horses, attached to a plough on moderate ground, exerted each a force of 150, Fr.-Amontons. We may suppose that they went a little more than two miles an hour, for eight hours...

A horse draws with the greatest advantage when the line] of direction is level with his breast; and he can draw with a force of 200 pounds, 24 miles an hour, for eight hours in the day

The mean draught of four horses was 36 myriogrammes cach, or 794 pounds.-Regnier. This must have been momentary. Supposing the velocity two feet in a second, the action would have been....

With a force of 240 only six hours. On a carriage, indeed, where friction alone is to be overcome, a middling horse will draw 1000 pounds.-Desaguliers

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By means of pumps a horse can raise 250 hogsheads of water, 10 feet high, in an hour.-Smeaton's Reports

A horse can in general draw no more up a steep hill than three men can carry; that is, from 450 to 750 pounds; but a strong horse can draw 2000 pounds up a steep hill, which is but short. The worst way of applying the force of a horse, is to make him carry or draw up hill; for if the hill be steep, three men will do more than a horse, each man climbing up faster with a burden of 100 pounds weight, than a horse that is loaded with 300 pounds: a difference which is owing to the position of the parts of the human body being better adapted to climb than those of a horse.

On the other hand, the best way of applying the force of a horse, is an horizontal direction, wherein a man can exert least force; thus a man, weighing 140 pounds, and drawing a boat along, by means of a rope coming over his shoulders, cannot draw above 27 pounds, or exert above one-seventh part of the force of a horse employed to the same purpose.

The very best and most effectual posture in a man is that of rowing; wherein he not only acts with more muscles at once for overcoming the resistance than in any other position. but as he pulls backwards, the weight of his body assists by way of lever.-Desaguliers.

The diameter of a walk for a horse-mill ought to be at least 25 or 30 feet.-Desaguliers.

Some horses have carried 650 or 700 pounds, seven or eight miles, without resting, as their ordinary work; and a horse at Stourbridge carried eleven hundred weight of iron, or 1232 pounds, for eight miles.-Desaguliers, Experimental Philosophy, vol. i.

Cazanel says, that a mule works in the West Indies two hours out of about 18, with a force of about 150 pounds, walking three feet in a second.-Dr. Young's Philosophy 4,5

2h 40' 1,2

These examples exhibit the great advantages which may be gained by directing the exertion of animals in a proper course, their effects being plainly reducible to the operations of mechanical powers. To describe the various modes of applying animal strength, as a first mover of mechanical engines, would greatly exceed our limits; we shall therefore merely state, that the most common machine for receiving the force of animals is the horse-walk, which affords the means of applying the action of that animal to create rotative motion. The horse-walk is formed of an horizontal lever or arm, attached to an upright spindle. The lever should not be less

than twelve feet, as the labour of the animal is greatly increased by a small curve, which causes an unequal resistance upon his two shoulders. The machine should be so regulated that the horse may not be required to deviate from his usual pace of two miles and a half, with a burthen, an hour. The gives, in which the horse works, should not be immovably fixed to the arms, but hung by a swivel joint, so that he may place himself in the most comfortable position, The work should be supplied to the machinery as regularly as possible.

Having, in the preceding account, stated the mean results of human exertion when applied to regular and uniform. labour, we shall in the next place proceed to notice some extraordinary feats of strength, as well as some that had the appearance of being such, but which were, in reality, the mere effects of contrivance and skill, and which might have been performed by almost any men who were possessed of that knowledge of their construction as would enable them similarly to exert their strength to the best advantage,

M. de la Hire, in an Examination of the Force of Men, (vide Memoirs of the Academy of Sciences for 1699,) says, There are men whose spirits flow so abundantly into their muscles, that they exert three or four times more strength than others do; and this seems to be the natural reason of the surprising strength that we see in some men who carry and raise weights which two or three ordinary men can hardly sustain, though these men be sometimes but of a moderate stature, and rather appear weak than strong. There was a man in this country a little while ago, who would carry a very large anvil, and of whom was reported several wonderful feats of strength. But I saw another at Venice, who was but a lad, and did not seem able to carry above forty or fifty pounds, with all possible advantages; yet this young fellow, standing upon a table, raised from the earth, and sustained off the ground, an ass, by means of a broad girth, which, going under the creature's belly, was hung upon two hooks that were fastened to a plat of small cords coming down in tresses from the hair on each side of the lad's head, which were in no great quantity. And all this great force depended only upon the muscles of the shoulders and those of the loins: for he stooped at first whilst the hooks were fastened to the girth, and then raised himself, and lifted up the ass from the ground, bearing with his hands upon his knees. He raised also in the same manner other weights that seemed heavier, and used to say he did with

more ease, because the ass kicked and struggled when first lifted from the ground."

Dr. Desaguliers, in some annotations upon De la Hire's paper, says, "What he attributes here to the muscles of the loins, were really performed by the extensors of the legs; for the young man's stooping with his hands upon his knees was not with his body forwards and his knees stiff, but his body upright and his knees bent, so as to bring the two cords with which he lifted to be in the same plane with his ancles and the heads of his thigh-bones; by which means the line of direction of the man and the whole weight came between the strongest part of his two feet, which are the supports: then as he extended his legs he raised himself, without changing the line of direction. That this must have been the manner I am pretty well assured of, by not only observing those that perform such feats, but having often tried it myself. As for the muscles of the loins, they are incapable of that strain, being above six times weaker than the extensors of the legs; at least I found them so in myself.

"About the year 1716, having the honour of showing a great many experiments to his late majesty King George I., his majesty was desirous to know whether there were any fallacy in those feats of strength that had been shown half a year before by a man, who seemed by his make to be no stronger than other men: upon this I had a frame of wood made to stand in, (and to rest my hands upon,) and with a girdle and chain lifted an iron cylinder, made use of to roll the garden, sustaining it easily when once it was up. Some noblemen and gentlemen who were present tried the experiment afterwards, and lifted the roller; some with more ease, and some with more difficulty, than I had done. This roller weighed 1,900 pounds, as the gardener told us. Afterwards I tried to lift 300 pounds with my hands, (viz., two pails with 150 pounds of quicksilver in each,) which I did indeed raise from the ground, but strained my back so as to feel it three or four days; which shows that, in the same person, the muscles of the loins (which exerted their force in this last experiment) are more than six times weaker than the extensors of the legs; for I felt no inconveniency from raising the iron roller.

During the time that Dr. Desaguliers was occupied in printing the second volume of his Philosophy, a man of great natural strength exhibited himself in London, of whom the doctor gives the following account.