KINETIC OR MECHANICAL VIEW OF NATURK. 91 



view, destined to become idtiinately merely chaptei-s in 

 dynamics as the doctrine of mechanical motion. 



A similar reluctance to look upon the vibrations of the 

 luminiferous ether merely as a convenient symbolism, as a 

 crude method of visualising molecular processes, which in 

 reality we cannot picture to ourselves, does not seem to 

 have troubled the minds of the great propounders of the 

 undulatory theory of light — i.e., of tlie elastic sohd 

 theory, as it is now termed in contradistinction to the 

 electro-magnetic theory propounded by Maxwell. The 

 greatest living exponent of the former view. Lord Kelvin, 

 who in his Baltimore Lectures grappled witli tlie dilli- 

 culties which still beset that view — falling back on the 

 principle of optical consonance and resonance, suggested 

 by Professor Stokes to explain some of the interactions of 

 the ether and ponderable matter : upon the theory of free 

 and forced vibrations, suggested by Bessel and Sellmeier ; 

 and on liis own fruitful suggestion of the vortex atom 

 to explain some of the properties of ponderable atoms 

 moving in the continuum which fills all space — expresses .'.r.. 



• 1 1 • Lord Kelvin 



himself very dehnitely on this point. " We must not <"' *•"? 



•^ "^ ^ vibrations 



listen to any suggestion that we may look upon the "f the ether, 

 luminiferous ether as an ideal way of putting the thing. 

 A real matter between us and the remoter stars I believe 

 there is, and that light consists of real motions of that 

 matter, motions just such as are described by Fresnel and 

 Young, motions in the way of transverse vibrations. If 

 I knew what the magnetic theory of light is, I might be 

 able to think of it in relation to the fundamental 

 principles of the wave theory of light, liut it seems to 

 me rather a backward step from an absolutely definite 



