Men and Horses In moving Machines. 283 



of the velocity of the motive force to the resistance. This 

 was the reason that long ago induced them to take the 

 trouble of determining the strength as well as velocity ex- 

 erted by men and animals when they are made to move 

 machinery ; and the results they obtained, which have been 

 commonly made use oi in computing the effect of machines, 

 are, that men exert from 27 to 30 lbs. with a velocity of 

 from li to 2 leet per second ; and that a horse has about 

 seven times more strength than a man, with a velocity of 

 from 4 to 6 feet per second. 



These are the data which we have been obliged to use 

 whenever it became necessary to compute the tffect of a 

 machine moved by men or horses. It is evident that the 

 force must be diminished when the velocity is increased, 

 and vice versa: but we are not yet certain of the method of 

 finding the ratio of the diminution or augmentation of this 

 force to the velocity. Euler has given us two different for- 

 mulae to compute this ratio; but no one has hitherto at- 

 tempted to verify by experiment, which of ihem is to be 

 preferred, although they differ very considerably from each 

 other. If we put P for the absolute force which takes 

 place when we simply consider equilibrium, C the absolute 

 velocity which takes place when the man or animal moves 

 freely and without being overcome by the resistance; p the 

 relative force, and c the corresponding velocity, we have 

 by the first of these fbrmul£e. 



Whereas the second gives us 



As I am obliged now more than ever to attend to a num- 

 ber of machines, and to compute their effect, it therefore 

 concerns me very much to know exactly in what manner 

 to estimate, compare, and fix the strength and velocity of 

 men and animals which are used for moving various ma- 

 chines proper for different purposes. 



With this view I made with considerable care the ex- 

 periments I am nov^/ about to detail ; which of course would 

 have been very expensive, had it not been for some facilities 

 which other persons may not possess. 



To make the experiments on human strength, I took 

 promiseufMisly 20 men of different sizes and constitutions, 

 whom I measured and weighed; the result of which is 

 given in the following Table : 



T 2 Table 



