50 THE FOUNDATIONS OF SCIENCE 



our bodies and minds, for preferring a mechanical 

 explanation rather than an electrical one. To explain 

 everything in terms of aether is but to shift the 

 mystery of the physical universe on to the concep- 

 tion of a medium itself hypothetical. 



Nevertheless, such a unification of physics, could 

 it be attained, would fulfil the highest aim of pure 

 science. Metaphysics is concerned with the ulti- 

 mate nature of reality, but the more modest aim of 

 science is the construction of a consistent model of 

 phenomena and their relations a model which shall 

 be logically consistent when examined by our minds, 

 and consistent, according to its own convention, with 

 the observed appearances of Nature. Any simpli- 

 fication in that model is a step in advance, and a 

 unity such as that of which glimpses are now vouch- 

 safed to us would satisfy our legitimate desires for 

 scientific knowledge. 



But it is not certain that unity will be obtained by 

 the conception of a luminiferous aether, which for 

 half a century has dominated physical science. It 

 is possible that the field of electro-magnetic energy 

 surrounding an electric charge in motion moves with 

 it, and that the vibrations of light travel through 

 this moving field, instead of through an ocean of 

 stagnant sether. These ideas, and the so-called 

 Principle of Relativity arising out of them, may be 

 the direction in which unity is next to be sought. 



