400 



PHILOSOPHICAL THOUGHT. 



69. 



Superses- 

 sion of as- 

 tronomical 

 view. 



60 



Plenum 

 substituted 



able processes, which afford to our understanding a 

 3onvenient resting-place, a temporary and provisional 

 foundation upon which to build. But this aspect upon 

 which the astronomical view of nature is based, which 

 governs almost half the exact science of the nineteenth 

 century, and which still enjoys popular favour, was in 

 the course of the century dispelled or superseded by the 

 theory of action by contact. According to this view, 

 empty space disappeared in the imagination of natural 

 philosophers, a plenum being put in the place of the 

 vacuum of intermediate space. This change of aspect, 

 which was brought about mainly through the study of 

 the phenomena of radiation, may be identified with the 

 name of Faraday. To him and his school it seemed 

 more natural to reduce mechanical action to processes 

 in the immediate vicinity of the acting centres, and they 

 accordingly filled empty space with an imaginary 

 something called ether, and undertook the very fruitful 

 task of defining in terms of measurable quantities the 

 properties and the behaviour of this all-pervading sub- 

 stance or entity. What we may call the second school 

 of French mathematicians after Laplace, those who were 

 largely influenced by Fresnel's discoveries, adopted an 

 intermediate position, looked upon the ether as an atomic 

 structure, and attempted to explain the movements of 

 this structure on the same lines as physical astro- 

 nomy liad followed in the calculation of cosmic pheno- 

 mena. They employed attractive and repulsive forces 

 acting at very small distances, as astronomers had used 

 them at very large distances. This remnant of the 

 astronomical view was finally destroyed in the school of 



