l LAW; — ITS DEFINITIONS. 71 



When the operations of any material Force can 

 be reduced to rules so definite as those which 

 have been discovered in respect to the Force of 

 Gravitation, and when these rules are capable of 

 mathematical expression and of mathematical 

 proof, they are, so far as they go, in the nature of 

 pure truth. Mr Lewes, in his very curious and 

 interesting work on the Philosophy of Aristotle, 

 has maintained that the knowledge of Measure — or 

 what he calls the "verifiable element" in our know- 

 ledge — is the element which determines whether 

 any theory belongs to Science, strictly so called, or 

 to Metaphysics ; and that any theory may be trans- 

 ferred from Metaphysics to Science, or from Science 

 to Metaphysics, simply by the addition or with- 

 drawal of its "verifiable element." In illustration of 

 this, he says that if we withdraw, from the Law of 

 Universal Attraction, the formula " inversely, as the 

 square of the distance, and directly as the mass," 

 it becomes pure Metaphysics. If this means 

 that, apart from ascertained numerical relations, 

 our conception of Law, or our knowledge of natu- 

 ral phenomena, loses all reality and distinctness, I 

 do not agree in the position. The idea of natural 



