326 Models of the Aetker. 



and cannot be destroyed ; so that if, as Thomson* suggested in 

 1867, the atoms of matter are constituted of vortex-rings in a 

 perfect fluid, the conservation of matter may be immediately 

 explained. The mutual interactions of atoms may be illustrated 

 by the behaviour of smoke-rings, which after approaching each 

 other closely are observed to rebound : and the spectroscopic 

 properties of matter may be referred to the possession by 

 vortex-rings of free periods of vibration. f 



There are, however, objections to the hypothesis of vortex- 

 atoms. It is not easy to understand how the large density of 

 ponderable matter as compared with aether is to be explained ; 

 and further, the virtual inertia of a vortex-ring increases as its 

 energy increases ; whereas the inertia of a ponderable body is, 

 so far as is known, unaffected by changes of temperature. It 

 is, moreover, doubtful whether vortex-atoms would be stable. 

 " It now seems to me certain," wrote W. Thomson^ (Kelvin) in 

 1905, " that if any motion be given within a finite portion of 

 an infinite incompressible liquid, originally at rest, its fate is 

 necessarily dissipation to infinite distances with infinitely small 

 velocities everywhere; while the total kinetic energy remains 

 constant. After many years of failure to prove that the motion 

 in the ordinary Helmholtz circular ring is stable, I came to the 

 conclusion that it is essentially unstable, and that its fate must 

 be to become dissipated as now described." 



The vortex-atom hypothesis is not the only way in which 

 the theory of vortex-motion has been applied to the construc- 

 tion of models of the aether. It was shown in 1880 by 

 W. Thomson that in certain circumstances a mass of fluid can 

 exist in a state in which portions in rotational and irrotational 



* Phil. Mag. xxxiv(1867), p. 15; Proc. R.S. Edinb. vi, p. 94. 



t An attempt was made in 1883 by J. J. Thomson, Phil. Mag. xv (1883), 

 p. 427, to explain the phenomena of the electric discharge through gases in terms 

 of tho theory of vortex-atoms. The electric field was supposed to consist in a 

 distribution of velocity in the medium whose vortex-motion constituted the atoms 

 of the gas ; and Thomson considered the effect of this field on the dissociation and 

 recoupling of vortex-rings. 



J Proc. Roy. Soc. Edinb., xxv (1905), p. 565. 



Brit. Assoc. Rep., 1880, p. 473. 



