404 GROVE'S CORRELATION OF PHYSICAL FORCES. 



laid down during the last two centuries in treatises on dynamics, not one of 

 these, except perhaps chemical affinity, can be admitted as a force. According 

 to that definition, " force is that which produces change of motion, and is 

 measured by the change of motion produced." 



Newton himself reminds us that force exists only so long as it acts. Its 

 effects may remain, but the force itself is essentially transitive. Hence, when 

 we meet with such phrases as Conservation of Force, Persistence of Force, 

 and the like, we must suppose the word Force to be used in a sense radically 

 different from that adopted by scientific men from Newton downwards. In all 

 these cases, and in the phrase "The Physical Forces" as applied to heat, we 

 are now, thanks to Dr Thomas Young, able to use the word Energy instead 

 of Force, for this word, according to its scientific definition as " the capacity 

 for performing work," is applicable to all these cases. The confusion has extended 

 even to the metaphorical use of the word Force. Thus, it may be a legitimate 

 metaphor to speak of the force of public opinion as being brought to bear on 

 a statesman so as to exert an overpowering pressure upon him, because here 

 we have an action tending to produce motion in a particular direction ; but 

 when we speak of "the Queen's Forces," we use the term in a sense as 

 unscientific as when we speak of the Physical Forces. The author, in his con- 

 cluding remarks, points out the confusion of terms which embarrassed him in 

 his endeavours to enunciate scientific propositions, on account of the imper- 

 fection of scientific language. This, he tells us, " cannot be avoided without a 

 neology which I have not the presumption to introduce or the authority to 

 enforce." 



Such a confession, proceeding from so great a master of the art of " putting 

 things," is a most valuable testimony to the importance of the study and 

 special cultivation of scientific language ; and a comparison of many passages in 

 the essay with the corresponding statements in more recent books of far inferior 

 power, will shew how much may be gained by the successful introduction of 

 appropriate neologies. What appeared mysterious and even paradoxical to the 

 giant, labouring among rough-hewn words, dwindles into a truism in the eyes 

 of the child, born heir to the palace of truth, for the erection of which the 

 giant has furnished the materials. 



Thus the appropriation of the word " Mass " to denote the quantity of 

 matter as defined by the amount of force required to produce a given accelera- 

 tion, has placed the students of the present day on a very different level from 



