Cor. Hence the effect of animal forco, or the quantity of work done 

 iin a given time, will be proportional to W r, or to P v (\ j , and 



c 4 P 



will be a maximum when y -^, and W = -^ , i. <?. when the animal 



moves with one-third of the speed with which it is able only to move it- 

 self, and is loaded with -^ of the greatest load it is able to put in motion. 



3. The quantities P and o, can only be determined by experience. Eu- 

 ler supposes that for the work of men, P may upon an average be taken 

 601b, and c = 6 feet per second, or a little more than four miles an 

 hour. 



4. A man, according to this estimate, when working to the greatest; 

 advantage, should carry a load of 271b, and walk at the rate of two feet 

 in a second, or a mile and one-third an hour. 



5. A horse, according to Desaguliers, drawing a weight out of a well, 

 over a pulley, can raise 200lb. for eight hours together, at the rate of 2 

 miles an hour. Supposing in this case the horse to work to the greatest 

 advantage, P 450, and c 6f miles per hour. This estimate, however, 

 seems to give too high a value to P. It will suit better with general ex- 

 pwience to make P = 420 and c = 7. 



6. It appears from Cavallo, that a horse can draw 25 ewt. on a level 

 road in a cart weighing 10 cwt., with wheels six feet high. In a com- 

 mon cart, two horses easily draw 30 cwt. In a common waggon, six 

 horses draw 80 cwt. : in three carts they might draw 90 ; in six, 150 cwt. : 

 and three carts cost less than a waggon. A horse drew three tons up a 

 railway rising 7 inches in 141 : the draught was 327 pounds besides fric- 

 tion. ( Yo ung's Nat. Phil) 



7. According to Coulomb's experiments on this subject, if w be the, 

 weight of the man's body, I an additional load, which he is made to car- 

 ry, H the height to which he ascends in a given time, when walking 

 freely, and h the height to which he ascends in the same time with the 

 load/; then 



h - 



w -f I 

 Cor. 1. When / - 2 w t L - o, 



Cor. 2. The greatest effect of a man's strength in raising a weight will 

 be, when the weight of the man is to that of his load as 1 : 1 -f- \/~$ t ^ 

 jiearly as 4 I 3. 

 9 



