SOME VIEWS ON LORD KELVIN'S WORK 423 



pressible frictionless liquid acted on by no forces, and that 

 material phenomena of every kind depend solely on motions 

 created in this liquid." As the investigation proceeded, it 

 branched off into a long series of additions to General Hydro- 

 dynamics, including Motion of Solids through a Liquid, Motion of 

 a Viscous Fluid, Turbulent Motion of an Inviscid Fluid, and 

 followed later by Wave Motion in Dispersive Media and Waves 

 on Water. 



The memoir on Vortex Motion, with the underlying idea 

 of all material properties being ultimately due to motion, taken 

 with the series of investigations in Molecular Theory to which 

 it gave rise, virtually introduces us to modern molecular theory 

 and carries us almost as far forward in forming a mental picture 

 of the world of atomic actions as it is possible to go without 

 the knowledge of the electron. Its immediate effect was to lead 

 Lord Kelvin on to a vigorous attack on a host of hydrodynamical 

 problems connected with vortex filaments and their stability, 

 and with the motion of free solids through a liquid. Associated 

 with this work came the completion and publication in 1871 of 

 the memoir, partly written in 1849, on the Mathematical Theory 

 of Magnetism — now much enriched by the hydrokinetic ana- 

 logies arising from his hydrodynamical investigations. The 

 questions of stability of various configurations of vortices 

 have reappeared again in connection with the modern electron 

 theory, and have led to important results. Difficulties of the 

 vortex atom theory arose, however, in connection with the 

 velocity of sound in gases, and with the relation of inertia to 

 temperature, and in the explanation of chemical combinations 

 and atomic weights. The advance of the atomic theory of 

 electricity, and the impossibility, in Lord Kelvin's view, of 

 accounting, by the aid of the vortex theory alone, for the infinite 

 variety of chemical substances, crystalline configurations, or elec- 

 trical or chemical or gravitational forces, led to his abandoning 

 it ; but not before the investigation had opened up possibilities 

 of accounting for the properties required in a medium capable 

 of producing electromagnetic actions by some complex foun- 

 dation of vortex motion in a liquid. In this connection it led 

 to extended efforts " to construct, by giving vortex motions to 

 an incompressible inviscid liquid, a medium which shall transmit 

 waves of laminar motion as the luminiferous ether transmits 

 waves of light," an idea advocated for many years by Fitzgerald. 

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