72 THE REIGN OF LAW. 



Forces is quite separate from any ascertained 

 measure of their energy. The knowledge, for 

 example, that all the particles of matter exert an 

 attractive force upon each other, is, so far as it 

 goes, true physical knowledge, even though we 

 did not know the further truth that this force acts 

 according to the numerical rule ascertained by 

 Newton. To banish from physical Science, pro- 

 perly so called, and to relegate to Metaphysics 

 all knowledge which cannot be reduced to nu- 

 merical expression, is a dangerous abuse of lan- 

 guage. 



Force, ascertained according to some measure 

 of its operation — this is indeed one of the defi- 

 nitions, but only one, of a scientific Law. The 

 discovery of laws in this sense is the great quest of 

 Science, and the finding of them is one of her great 

 rewards. Such laws yield to the human mind a 

 peculiar delight from the satisfaction they afford to 

 those special faculties whose function it is to recog- 

 nise the beauty of numerical relations. This satis- 

 faction is so great, and in its own measure is so 

 complete, that the mind reposes on an ascertained 

 law of this kind as on an ultimate truth. And 



