16 Sir William Thomson on Vortex Atoms. 



any of the properties of matter without attributing them to the 

 atom itself. Thus the " clash of atoms/' as it has been well 

 called, has been invoked by his modern followers to account for 

 the elasticity of gases. Every other property of matter has simi- 

 larly required an assumption of specific forces pertaining to the 

 atom. It is as easy (and as improbable — not more so) to as- 

 sume whatever specific forces may be required in any portion of 

 matter which possesses the " Wirbelbewegung/' as in a solid in- 

 divisible piece of matter ; and hence the Lucretius atom has no 

 prima facie advantage over the Helmholtz atom. A magnificent 

 display of smoke-rings, which he recently had the pleasure of 

 witnessing in Professor Tait's lecture-room, diminished by one 

 the number of assumptions required to explain the properties of 

 matter on the hypothesis that all bodies are composed of vor- 

 tex atoms in a perfect homogeneous liquid. Two smoke-rings 

 were frequently seen to bound obliquely from one another, sha- 

 king violently from the effects of the shock. The result was very 

 similar to that observable in two large india-rubber rings striking- 

 one another in the air. The elasticity of each smoke-ring seemed 

 no further from perfection than might be expected in a solid 

 india-rubber ring of the same shape, from what we know of the 

 viscosity of india-rubber. Of course this kinetic elasticity of 

 form is perfect elasticity for vortex rings in a perfect liquid. It 

 is at least as good a beginning as the " clash of atoms " to ac- 

 count for the elasticity of gases. Probably the beautiful inves- 

 tigations of D. Bernoulli, Herapath, Joule, Kronig, Clausius, 

 and Maxwell on the various thermodynamic properties of gases, 

 may have all the positive assumptions they have been obliged to 

 make, as to mutual forces between two atoms and kinetic energy 

 acquired by individual atoms or molecules, satisfied by vortex 

 rings, without requiring any other property in the matter whose 

 motion composes them than inertia and incompressible occupa- 

 tion of space. A full mathematical investigation of the mutual 

 action between two vortex rings of any given magnitudes and 

 velocities passing one another in any two lines, so directed that 

 they never come nearer one another than a large multiple of the 

 diameter of either, is a perfectly solvable mathematical problem ; 

 and the novelty of the circumstances contemplated presents diffi- 

 culties of an exciting character. Its solution will become the 

 foundation of the proposed new kinetic theory of gases. The 

 possibility of founding a theory of elastic solids and liquids on 

 the dynamics of more closely- packed vortex atoms may be rea- 

 sonably anticipated. It may be remarked in connexion with this 

 anticipation, that the mere title of Rankine's paper on " Mole- 

 cular Vortices/' communicated to the Eoyal Society of Edinburgh 

 in 1849 and 1850, was a most suggestive step in physical theory. 



