MEANING OF THE TERM "FORCE." 333 



at rest, is caused to move with the (uniform final) velocity c / 

 from the knowledge of the magnitudes M and c it is certainly 

 possible to deduce the value of the product of the force (in 

 Newton's sense) into its effective space, but we are not thereby 

 enabled to conclude as to the magnitude of this force itself. 



As a matter of fact, the necessity soon made itself felt of 

 treating and naming this product as a whole. It also has 

 been called " force," and the expressions " vis viva of motion," 

 " moving force," *' working force," " horse-power " (or force), 

 " muscular force," &c., have been long naturalized in science. 



However happy we may, in many respects, think the 

 choice of this word, there is still the objection that a new 

 meaning has been fixed upon an already existing technical 

 expression, without the old one having been called in from 

 circulation at the same time. This formal error has become 

 a Pandora's box, whence has sprung a Babylonian confusion 

 of tongues. 



Under existing circumstances no choice is left us but to 

 withdraw the term " force" either from Newton's dead force 

 or from Leibnitz's living force ; but in either case we come 

 into conflict with prevailing usage. But if once we have 

 made up our minds to introduce into our science a logically 

 accurate use of terms, even at the cost of existing expressions 

 which have become easy and pleasant to us by long usage, we 

 cannot long hesitate in the choice we have to make between 

 the conceptions I. and II. 



Let us consider the elementary case of a mass, originally 

 at rest, which receives motion : this happens, as has been al- 

 ready said, by the mass being subjected to a certain push or 

 pull under the influence of which it traverses a certain space, 

 the effective space. Now, however, both the velocity and 

 also the intensity of the push (Newton's force) always vary 

 at every point of the effective space ; and in order to mul- 

 tiply these variable magnitudes into effective space, that is, 

 to deduce the quantity of motion from the intensity of the 



