SCIENCE AS A SYMBOL AND A LAW 21 



stituted, in an occult way, of modifications of me- 

 chanical motion and force, let us attempt to frame laws 

 which shall embrace the properties common to any one 

 class. He finds energy, or the capacity to effect 

 changes, to be the common characteristic of the various 

 states of matter to which the several branches of 

 physics relate. If then we frame general laws regard- 

 ing energy, we shall be able to apply them, with appro- 

 priate changes, to every branch of physics. 



Rankine evidently denies the advisability of trying 

 to find the cause of the attraction of bodies for one 

 another, or the mechanism of the propagation of light 

 and heat through empty space. In all cases we have a 

 certain quantity of energy, acting in a specific manner. 

 Our aim should be to find by experiment the properties 

 of any such manifestation, and to combine all common 

 properties by general mathematical laws. Such was 

 the method of Newton when he established the law of 

 universal gravitation and refrained from publishing 

 how the forces of attraction could act through space, 

 and no discovery has aided science more. But after he 

 had determined experimentally many of the laws of 

 light, he advanced the hypothesis that these phenomena 

 were caused by motions of intangible corpuscles and he 

 ventured so far as to describe the shape and properties 

 of these hypothetical bodies. It is claimed, on good 

 grounds apparently, that his corpuscular theory retarded 

 the growth of the subject for more than a century, by 



