ENERGY IN GENERAL. 75 



Now what real thing could pass instantly from infinity 

 to zero? 



That skilful and very able physiologist, M. Chauveau, 

 has endeavoured to use the same term energy of con- 

 traction for the two phenomena of effort (force) and 

 work. It seems, however, from the point of view of 

 the expenditure imposed on the organism, that these 

 two modes of activity, static contraction (effort), and 

 dynamical contractiott (work), may be, in fact, perfectly 

 comparable. But although this manner of conceiving 

 the phenomena may certainly be exact, and may be 

 of great value, the idea of force must none the less 

 remain distinct from that of work. The persistence 

 of the author in violating established custom in this 

 connection has prevented him from enabling mechani- 

 cians and even some physiologists to understand and 

 accept very useful truths. 



Power. — The idea of mechanical /^zt/^r differs from 

 those of force and work. The idea of time must 

 intervene. It is not sufficient, in fact, in order to 

 characterize a mechanical operation, to point to the 

 task accomplished. It may be necessary or useful to 

 know how much time it required. This is true, 

 especially when we are concerned with the circum- 

 stances as well as the results of the performance of 

 the work; and this is the case when we wish to 

 compare machines. We say that the machine which 

 does the work in the . shortest space of time is 

 the most powerful. The unit of power is the Kilo- 

 grammetre-second — that is to say, the power of a 

 machine which does a kilogrammetre in a second. In 

 manufactures we generally employ a unit 75 times 

 greater than this — a horse-power. This is the power of 

 a machine which does 75 kilogrammetres a second. 



