Iii his introduction to his liable, 1)r. Young observes, that to compare the dill rent estimates of moving power. it will be convenient to take an unit as the mean etleet of the labour of an active man, and a ithont impediment. This a ill be found, on a modwate estimation, sufficient to raise 101b. to the height of 10 feet in a second, for 10 hours in a day ; or to raise 1001b., which is the weight of twelve wine gallons of water, 1 foot in a second, or 30 000 feet in a day ; or 3,000.000I1., or 4:12,000 gallons, 1 foot in a day. This we may call a tii•ce of 1 continued :30,000." " Immediate Force rf Men without Deduction ,/)r Friction.
"And the force in a state of rest becomes 21. or about 70111.; with a velocity of two miles, 30ib.; w ith three, 2 1lb.; and with four, 151b.
It is obvious, that in the extreme cases this formula is inaccurate, but lbr moderate velocities, it is probably a teler aide approximation.
•• Coulomb makes the maximum of elThet alter a man, weighing 70 Idlogrammes, carries a weight of 531b. up stairs ; but this appears to be too great a load; he considers 145 kflogra mines as the greatest weight that can he raised, lle observes, that in Martinique, where the thermometer is sel dom below the labour of Europeans is reduced to one half.
"llarriot asserts that his pump, with a horizontal motion, enables a man to do one-third more work than the common punts, with a vertical motion.
" Porters carry from 2001h. to 3001b. at the rate of three miles an hour; •hail men walk four miles an hour with a load of 150Ib. each ; and it is sail that in Turkey, there are porters, mho, by stooping forward, carry from 700 to 9001b. placed very low on their backs.
`Die most advantageous weight for a man of common strength to carry• horizontally, is 1121b.; or, if he returns unladen, 1:151b. With wheelbarrows, men will do half as much more work as with hods. Coulomb.
" Performance of Men by Machines.
"A horse can in general draw no more up a steep It'll than three men can carry, that is, from 4501b. to 750Ib. ; bin a strong horse can d aw 2000Ib. up a steep hill, that is but short. The woist way of applying the tbree of a horse, is to make him carry or draw up hid ; if the hill be steep, three men will do more than a horse, each man climbing up faster with a burden of 100th. weight, than a horse that is loaded with :,00.h., a differenc:t arising from the position of the parts of the human body being better adapted to climbing than those of a horse.
On the other hand, the best way of applying the force of a horse, is in an horizontal direction, wherein a man can exert least force: thus a inan, weighing 1-101b., and drawing a
boat along by means of a rope coning over his shoulders, cannot draw above 271b., or exert alio% e one-seventh part of the since of a horse employed to the same purpose.
"Tile 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.—Desugtthers.
The diameter uf a wads fat a horse-mill, ought to be at least 25 or 3U feet.—Destrytdiers.
"Some horses have carried 650Ib. or 7001h. seven or eight miles without resting, as their ordinary \Yolk : and a horse at Stourbridge carried Itcwt. of iron, or 12:321b. for eight miles.—Destivuliers, Erp. Philos. i.
contin- Day's " Irurk of Hides. uation. Work.
Corrine/ says, that a mule works in the West Indies two hours. out of about with a force of about 1.50Ib. walking 3 feet in a second 4.4 2'' 40' 1.2 Foam loaniinote. to M. Coulomb. a wind mill with fun. sails. measuring till feet (French) from one extremity to that of the opposite sail, and 6 feet wide, or a little more. is capable of raising 10001b. (French) 218 feet in l' and of working on an average J hours in a day. This is equivalent to the work of 34 men, as it has been above estimated, 25 square feet of canvass performing about the daily \Yolk of a man.
"Robison says, that 1 cwt. of coals burned in a steam engine will raise at least 20,000 cubic feet of water 24 feet high ; this is equivalent to the daily labour of S.32 men. A steitin-engine in London, with a 24-inch cylinder. does the work of '72 horses, and consumes a cha'dron of coals in a day ; each bushel being equivalent to two horses, and each square inch of the cylinder performing nearly the work of a man.
"If we calculate the quantity of motion produced by gun powder, we shall find that this agent. though extremely con venient, is far more expensive than _human labour ; but the advantage of gunpowder consists in the great rarity of the acting substance. A spring or a bow can ()Illy act with a moderate velocity, on account of its own weight. The air of the atmo-phere,1u,wever compressed, could not flow into a vacuum with a velocity so great as 1,500 feet in a second. Hydrogen gas might move more rapidly, but the elastic sub stance produced by gunpowder is capable of propelling a very heavy cannonball with nmeh greater velocity.
" It is said, that nine tons of water. falling 10 feet, will grind and dress a bushel of wheat ; consequently a man might do the sante in 33' 36"."