CORRELATION OF PHYSICAL FORCES. 405 



those who had to puzzle out the meaning of the phrase Vis inertia by com- 

 bining the explanation of Vis as force, with that of inertia as laziness. In the 

 same way the word " stress " as an equivalent for " action and reaction," and 

 as a generic name for pressure, tension, &c., will save future generations a great 

 deal of trouble ; and the distinction between the possession of energy and the 

 act of doing work, which is now so familiar to us, would have obviated several 

 objections to the doctrine of the essay, which are founded on statements in 

 which the production of one form of energy and the maintenance of another are 

 treated as if they were operations of the same kind. We read at p. 163 : 

 Thus, "a voltaic battery, decomposing water in a voltameter, while the same 

 current is employed at the same time to make (maintain) an electromagnet, 

 gives nevertheless in the voltameter an equivalent of gas, or decomposes an 

 equivalent of an electrolyte for each equivalent of decomposition in the battery 

 cells, and will give the same ratios if the electro-magnet be removed." 



Here the maintenance of a magnet is a thing of a different order from 

 the decomposition of an electrolyte ; the first is maintenance of energy, the other 

 is doing work. This is well explained in the essay ; but if appropriate language 

 had been used from the first, the objection could never have been put into form. 



