ANIMAL STRENGTH. The subject of animal strength will continue to be of much importance as long as it shall be found ne cessary to employ men or animals, either in conveying burdens or in giving motion to machinery ; since by it the employer is enabled to ascertain what is the greatest quantity of useful work which may be obtained from such agents without subjecting them to a degree of fatigue which might in time prove injurious to their health or bodily powers.
With respect to men, Coulomb found that when a man travels unloaded on level ground he can walk 31 miles daily. Now, assuming the weight of a man to be 160 lbs., we have 160 X 31 or 4960 for the measure of his strength or the quantity of action, which is, consequently, equivalent to that of a machine capable of carrying 4960 lbs. to a distance of 1 mile, or 1 pound to a distance of 4960 miles in one day.
He found also, from a mean of the work done by the porters of Paris, that with a bur den equal to 128 lbs. a man can walk 9.72 miles in a day, from which it follows (the weight of a man being 160 lbs.) that the quantity of action is (160+128) X 0.72, or 2799. If the weight of the man be not in cluded, the quantity of action is 128 X 9.72, or 1244; and this is to be considered as the use ful effect. Subtracting 2799 from 4960, we have 2161 for the measure of the action lost in consequence of the burden; but the useful effect, which in the first case was nothing, is in the second expressed by 1244.
By means of a formula, which was given by Euler, with the data afforded by these expe riments, it is found that 272 lbs. constitute the greatest burden which a man of average strength can support, and under which he cannot move. It is found, moreover, that the useful effect is at a maximum when a man is loaded with 121 lbs.: under this burden he can walk 10-i- miles, nearly, in a day ; and consequently the greatest useful effect is ex pressed by 1280.
Coulomb further determined, that when a man ascends a convenient flight of steps un loaded, the vertical heights of all the ascents during one day being added together, were equal to 1.82 miles ; the quantity of action may therefore be expressed by 160 x 1.82 or 291, as if the action were equivalent to that of a machine which could raise 291 lbs. to the height of 1 mile vertically, or 1 lb. to the height of 291 miles during a day. When loaded with 1501bs. the vertical height ascended was 0.494 miles : the whole quantity of action is, therefore, in this case (160 +150) x 0.494, or 153, while the useful effect is 150 X0.401, or 74; that is, 74 lbs. raised 1 mile vertically.
It is remarkable that, from the result of Coulomb's experiments on the power of men ascending steps, both the greatest weight which a man can carry without moving, and the weight which he should bear to render his useful effect a maximum, are nearly the same in this case as they were found to be from expe riments made with burdens carried on level ground.
Coulomb has also made experiments to de termine the quantity of action in the case which most generally occurs when heavy goods are carried in towns, viz., that in which
a porter, having delivered his burden, returns unloaded for another; and his conclusion is, that, in order to produce the most useful effect in this case, the greatest burden which a man should carryon level ground is 135 lbs., and with this he should walk 7 miles. The quantity of useful action is therefore 135 X 7, or 945.
It is said that a London porter can carry 200 lbs. on his shoulders at the rate of 3 miles per hour; but this action can only be continued during a short time.
The following statements of the strength of men are taken from Hachette's Trait6 des Machines,' and from other sources; the nu merical values being reduced so as to express the number of pounds carried by a man one mile per day of eight hours :— lbs.
Drawing a vessel on a canal .. —753,159 Conveying a load (110 lbs.) in a wheel-barrow (1.018 miles per hour) 896 Drawing a small waggon on four wheels over rather unequal ground 857 Pulling horizontally, the weight being raised by a rope passing over a pulley 378 Rowing in a boat 371 Thrusting horizontally, as at a capstan 368 Turning a winch and axle 159 Digging with a spade A soldier marching (12•43 miles) with his arms, &c. (GO lbs.) daily 745 With respect to the horse, the most useful way of employing his strength is to make him draw loads in a cart or waggon ; but, even for such work, the estimates which have been made of the quantity of action performed daily are various.
According to Tredgold a horse can draw 125 lbs. at the rate of 21 miles per hour, which, for one day, would give 125 X21 x 8 or 2500. But Messrs. Bonbon and Watt ascer tained from trials, purposely made, that a strong horse can draw 125 lbs. at the rate of 3 miles per hour ; and the measure of the power of such a horse is 3000, which expresses a number of pounds drawn 1 mile in a day. If this be multiplied by the number of feet in a mile, and the product be divided by the num ber of minutes iu eight hours, the result (=33000) denotes a weight in pounds drawn 1 foot per minute during the eight hours ; and that result is now universally adopted as a measure of the power of a horse, and is called one horse-power.
The useful effect of a horse when walking in a circle, as in some mills, is considered as equivalent to 800 A horse carrying a soldier with arms, S.x.. (--=200 lbs.), can go 25 miles in a day, which gives WOO An African dromedary carrying only his rider (1601bs.) can go between 7 and 8 miles per hour during nine or ten hours, which gives 160X71 X91, or 11100 An Asiatic camel will carry bur dens weighing from 500 to 800 lbs. (suppose 600) at the rate of 21 miles per hour. This, for a day of eight hours, gives 600 X21 X8, or 12000 The velocity of a horse in walking is esti mated at 51 feet per second, or 3i miles per hour ; in trotting 12 feet per second, or 8 k miles per hour; and in galloping 18 feet per second, or 121 miles per hour.