72 



SCIENTIFIC THOUGHT. 



years old, but already acquainted with English experi- 

 mental and French mathematical researches, he pointed 

 out how phenomena of flow — i.e., of motion — could be 

 mathematically grasped by a formula quite similar to 

 that of the distribution of masses at rest and appar- 

 ently governed by attractive forces at a distance. For 

 instance, the distribution of temperature at various dis- 

 tinct points in a space in which a flow of heat from an 

 origin had brought about a stationary condition (the 

 equilibrium being dynamical, not statical), was mathe- 

 matically expressed by a formula identical with that 

 which, according to Poisson and others, gave the dis- 

 tribution of electrical or attracting masses. Now we 

 know that in the former case the equilibrium is main- 

 tained by a flow across the intervening space, which takes 

 time. This suggests, therefore, the possibility of ex- 

 plaining the so-called statical effects of attracting or 

 repelling masses kinetically by a process of flow or motion 

 going on in the intervening medium, a notion to which 

 Faraday clung tenaciously. In 1845 Thomson reverted 

 to this subject, and after harmonising the two views, 

 concluded by stating that the latter " method of establish- 

 ing the mathematical theory would be even more simple 

 if possible than that of Coulomb." ^ 



^ " On the Mathematical Theory 

 of Electricity in Equilibrium," 

 1845. See ' Reprint of Papers on 

 Electrostatics and Magnetism,' 2nd 

 ed. , p. 29. A study of these mathe- 

 matical researches of Lord Kelvin, 

 beginning early in the 'forties and 

 extending over more than twenty 

 years, is of special historical in- 

 terest, as showing the gradual 

 growth of a physical out of a purely 



mathematical theory : most of the 

 conceptions which have since be- 

 come general through Maxwell's 

 electro-magnetic theory, as it has 

 been developed and popularised 

 by subsequent writers (notably 

 Prof. Poynting, Prof. Oliver Lodge, 

 and Mr Oliver Heaviside), being 

 already contained in Thomson's 

 papers as mathematical notions. 

 Thomson is throughout careful to 



