REQUISITES OF LANGUAGE. 243 



misleading tendency of this mode of expression, 

 several of his remarks are so much to the purpose, 

 that I shall take the liberty of transcribing them. 



He observes*, that many of the controversies which 

 have had an important share in the formation of the 

 existing body of science, have " assumed the form of a 

 battle of Definitions. For example, the inquiry con- 

 cerning the laws of falling bodies, led to the question, 

 whether the proper definition of a uniform force is that 

 it generates a velocity proportional to the space from 

 rest, or to the time. The controversy of the vis viva was, 

 what was the proper definition of the measure of force. 

 A principal question in the classification of minerals 

 is, what is the definition of a mineral species. Physi- 

 ologists have endeavoured to throw light on their 

 subject by defining organization, or some similar 

 term." Questions of the same nature are still open 

 respecting the definitions of Specific Heat, Latent 

 Heat, Chemical Combination, and Solution. 



4 * It is very important for us to observe, that these 

 controversies have never been questions of insulated 

 and arbitrary definitions, as men seem often tempted 

 to imagine them to have been. In all cases there is 

 a tacit assumption of some proposition which is to be 

 expressed by means of the definition, and which gives 

 it its importance. The dispute concerning the defini- 

 tion thus acquires a real value, and becomes a question 

 concerning true and false. Thus in the discussion of 

 the question, What is a uniform force ? it was taken 

 for granted that gravity is a uniform force. In the 

 debate of the vis viva, it was assumed that in the 

 mutual action of bodies the whole effect of the force is 

 unchanged. In the zoological definition of species 



Phil, of the Tnd. Sc. ii., 177-9. 



R 2 



