1890-91.] THE LUMINIFEROUS ETHER. 97 



the same proportion to the radius of the particle (supposing it to be 

 spherical) as the unit volume of space is to the total volume of particles 

 contained in such unit volume " applies to the ether. From this beauti- 

 ful law many important and exceedingly interesting consequences follow, 

 but I shall not detain you by pointing them out. From the low density 

 of the ether taken in connection with the functions it has to perform, and 

 especially the necessity of the ether particles being able to penetrate 

 with freedom the intermolecular and interatomic spaces it follows that 

 the component particles of the ether must be extremely minute. 



The density of the ether being small, and its particles being minute, it 

 follows that in order to produce pressure necessary to effect the rapid 

 and stupendous changes observed in nature, the velocity of the component 

 particles of the ether must be correspondingly great. Green, in his 

 masterly treatment of the subject, has exhaustively worked out the wave 

 theory of light on the hypothesis that the medium is continuous and 

 homogeneous and nothing of moment has been added to what he has 

 done. But, as is well known, his results do not correspond with observed 

 facts, so that his explanations are unsatisfactory and incomplete. The 

 Undulatory Theory of Light as developed by him thoroughly explained 

 dispersion and absorption, but did not explain reflection and refraction at 

 plane surfaces, and what has aptly been called the hopeless difficulty of 

 double refraction in crystals, stands in the way of the final acceptance of 

 the theory as at present developed. 



No explanation of these difificulties has yet been given which can be 

 regarded as complete or satisfactory, and their solution is the work of 

 the future. 



It is quite obvious that their successful solution will throw a flood of 

 light on the whole question of the real nature of matter. 



