968 On the Strength of Men and Horses in moving Machines, 



mediately follows : I began these experiments with a weight 

 of l(X)ll)s. and increased it by 5 every time from that 

 number up to 400 lbs. 



I made this machine move by the seven first of my 

 ■workmen, placing ihem in such a wav thai their direction 

 remained almost always perpendicular to the arm on which 

 was attached the cord v\ hich passed over their shoulders iri 

 an almost horizontal direction. 



Thus situated, they niaJe 281 turns with this machine in 

 two hours, which eave for their relative velocity c = 2"43 

 feet per second. We have also the absolute force, or P, 

 from these 7 men, by the above Table = 730 lbs.: and 

 their absolute velocity or C — 5-30 feet. 



Therefore, by snbstiuning these values in the first for- 

 jnula, we find the relative force p = 203 lbs. which agrees 

 very well with what we have just found above. 



If instead of this first formula the second be taken, it 

 gives p = !53 lbs. which is far too little. 



By this it is evident, that the first of Euler's two for- 

 mulae is to be preferred in all respects. I have also made 

 a great number of combinations, and I almost always found 

 the same effect. 



Dividing the 205 lbs. which we have just found by 7 the 

 number of workmen, we get 29 lbs. for the relative lorce 

 with 2'45 feet relative velocity for each man, which is 

 rather more than the values commonly adopted in the com- 

 putation of machinery. A number of other observations 

 on different machines, which } intend to relate another 

 time, have given nie the same result; that is to say, we 

 must value the mean human strength at 29 or 30 lbs. with 

 a velocity of 2i feet per second. 



To obtain the ratio of the strength of a horse to that of 

 a man, I had the same machine moved by a horse without 

 altering any thing; and I found by ten diflerent horses 

 which I used successively, that a horse makes 603 turns 

 in 2 hours instead of 281 : therefore, by supposing the 

 static motion of a horse 7 times greater than that of a man, 

 we find that the former has 5-3 feet per seccaid of velo- 

 city. 



3y this it is evident, that the effect of a horse is 14 time? 

 greater than that of a man, or, which amounts to the same 

 thins, 14 men must be used in.-tead of I horse. Hence it 

 appears, that it is much more advantageous to employ 

 hor>es th.nn men in moving machines, if other reasons did 

 not require us to prefer men. 



