72 LIFE AND DEATH. 



Work. — The muscular activity of man may be 

 brought into play in yet another manner. When we 

 employ workmen, as Carnot said in his Essai sur 

 reqiiilibre et le inouvement, it is not a question of 

 " knowing the burdens that they can carry without 

 moving from their position," but rather the burdens 

 that they can carry from one point to another. For 

 instance, a workman may have to lift the water from 

 the bottom of a well to a given height, and the case is 

 the same for the animals we employ. " This is what 

 we understand by force when we say that the force of 

 a horse is equal to the force of seven men. We do 

 not mean that if seven men were pulling in one 

 direction and the horse in another that there would be 

 equilibrium, but that in a piece of work the horse 

 alone would lift, for example, as much water from the 

 bottom of a well to a given height as the seven men 

 together would do in the same time." ^ 



Here, then, we have to do with the second form of 

 muscular activity, which is called in mechanics, "work" 

 — at least, if in the preceding quotation we attach no 

 particular importance to the words " in the same 

 time," and retain the employment of muscular activity 

 only "under constant conditions." Mechanical work 

 is compared with the elevation of a certain weight to a 

 certain height. It is measured by the product of the 

 force (understood in the sense in which it was used 

 just now — that is to say, as causing or resisting motion) 

 and the displacement due to this motion. The unit is 

 the Kilogrammetre — that is to say, the work necessary 

 to lift a weight of one kilogramme to the height of 

 one metre. 



^ These words spoil the statement, for time has nothing to 

 do with it. 



