336 Models of the Aether. 



It is possible that hollow vortices are better adapted than 

 ordinary vortex-filaments for the construction of models of the 

 aether. Such, at any rate, was the opinion of Thomson (Kelvin) 

 in his later years.* The analytical difficulties of the subject are 

 formidable, and progress is consequently slow ; but among the 

 many mechanical schemes which have been devised to represent 

 electrical and optical phenomena, none possesses greater interest 

 than that which pictures the aether as a vortex-sponge. 



* Proc. Roy. Irish Acad., November 30, 1889 ; Kelvin's Math, and Phys. 

 Papers, iv, p. 202. "Rotational vortex-cores," he wrote, "must he absolutely 

 discarded ; and we must have nothing hut irrotational revolution and vacuous 

 cores." 



