MATTER, SPACE, AND TIME 233 



properties of the aether by familiar mechanical con- 

 ceptions. But it was realised that, even if such 

 a model were successfully constructed, it would 

 not necessarily represent the actual structure of 

 the aether ; that was not its object. The primary 

 function of such a model would have been to justify 

 our theory of the aether as expressed in Maxwell's 

 electro-magnetic equations, in the other equations 

 requisite to explain electric charges and currents, 

 and, if possible, to suggest an explanation of 

 gravitation also. 



And so a tendency arose to give up the old 

 elastic solid view of the aether, and to secure the 

 necessary rigidity in another way. A top when 

 spinning possesses rigidity of position. It main- 

 tains its vertical position against the effects of 

 its weight, and any displacement from the vertical 

 is followed by definite oscillations around the 

 mean position. These phenomena can best be 

 studied in the gyroscope, which first found a 

 practical application in the Whitehead torpedo, 

 where a direct course is kept by the tendency of 

 a spinning wheel to maintain its axis of rotation 

 undeviated. On these principles, Lord Kelvin 

 and others described a gyrostatic aether, in which 

 the rigidity is secured by the motion of some still 

 more primal material. The aether was perhaps 

 composed of a number of interlacing vortex 

 filaments ; its structure might be fibrous like 

 that of a bundle of hay. 



Following the line of thought Indicated by 

 Lord Kelvin with his conception of the vortex 

 atom, we conceived matter to be an aethereal 

 manifestation. But the simple vortex ring Itself 

 soon failed to meet the demands made upon it. 



