428 SCIENCE PROGRESS 



ditions for atoms and electrons, when undisturbed by collisions. 

 The difference was not wholly due to the fact that static con- 

 ditions lend themselves to a simpler discussion. It is natural, 

 however, that experimentalists should prefer a stable configura- 

 tion of motion, as no doubt the aspect of motion is the one 

 most prominently before them. All speculations in this direc- 

 tion are at present merely tentative suggestions awaiting 

 confirmation. It is interesting to find, however, Lord Kelvin's 

 latest description of the atom, given at the British Association 

 Meeting at Leicester 1907, as a gun loaded with an explosive 

 shell, recurring in another connection {Phil. Mag., October 



I9i3» P- 579). 



Turning now to the other section of Lord Kelvin's work 



referred to above, which occupied his attention from 1886 onwards, 

 but more especially in his later years, we shall find that it is 

 complementary to the papers just discussed. The section of his 

 work included under the title Waves on Water, containing as it 

 does some of his most beautiful applications of the Fourier 

 analysis which attracted him so much in his student days, recalls 

 his early intimacy with the writings of the French mathematical 

 school, especially those of Cauchy and Poisson. For the begin- 

 nings of this series of investigations in his own writings, we 

 have to go back to the early papers on Hydrodynamics contri- 

 buted in conjunction with Stokes to the Cambridge Mathe- 

 matical Journal before 1849. Hydrodynamical analogies are 

 continually appearing in his work on Magnetism and Elasticity 

 and Electric Currents, and, as we have seen above, in his philoso- 

 phic speculations on matter. A group dealing with diffusion 

 forms the subject of a separate paper in vol. iii. The influence 

 of Stokes' Hydrodynamical Papers— on the application of the 

 Method of Images, on waves and on the work against viscosity 

 of water required to maintain a wave — no doubt accounts largely 

 for his special interest in purely hydrodynamical waves pro- 

 blems. The experiments of Froude on resistance experienced 

 by models towed through water, and Lord Kelvin's own acquaint- 

 ance with the sea in cable and yachting expeditions, brought him 

 directly in contact with the problems of ship waves and the action 

 of wind in generating waves at sea. 



The earlier papers of the group all belong to the purely 

 hydrodynamical aspect of the subject. In 1871 he gave the 

 theoretical explanation of the influence of wind and of surface 



