422 SCIENCE PROGRESS 



mind : " I have no faith in speculations of this kind unless they 

 can be reduced to regular analysis." Overcaution and entire 

 avoidance of speculation not warranted by the analysis delayed 

 his full acceptance of the teaching of Joule. The absence of a 

 definite physical basis for the formulas brought forward by 

 Maxwell was an impassable barrier to Lord Kelvin's acceptance 

 of them as substantial theory, in spite of their power to meet the 

 facts. Wherever an element of uncertainty remained, as in 

 the application of the Boltzmann Maxwell Law, or with regard 

 to pressure of radiation and the manner in which thermodynamics 

 was employed in the theory of that subject, his attitude was one 

 of entire distrust. 



The explanations, inspired by Faraday's discovery of 1845, °f 

 Electrostatic, Magnetic, and Electromagnetic forces by various 

 types of Strain in an elastic solid, and the Dynamical illustration 

 which he provided in 1856 for the action of Magnetism on Light 

 and for the rotary action of transparent bodies on polarised 

 light, are typical examples of his requirements in the way of 

 satisfactory explanation. The latter paper led ultimately to the 

 analogy for ether of a fluid constituted of imbedded gyrostats ; 

 but being, in the years immediately preceding 1856, engrossed 

 with the difficulties of reconciling Carnot and Joule and, later, 

 with the application of the principles of thermodynamics to 

 gases, to electrolysis, to thermoelectricity, to magnetism and other 

 subjects, and with the development of the doctrine of available 

 energy, he naturally did not regard the realising of his " grand 

 object " as an object for immediate pursuit. His constant appeal 

 to analogy, however, in his writings of this period bears 

 testimony to his constant review of the range of mathematical 

 analysis to discover the most promising line of advance towards 

 his object. And when the tide of his thermodynamic researches 

 had spent its first rush in the full stream of investigation 

 emanating from the two great energy principles, and when other 

 interests could reassert their claims, the appearance of Helm- 

 holtz memoir on the dynamical theory of Vortex Motion in 1858 

 inspired him to fresh efforts to accomplish his original aim. 

 The promise of success which the vortex atom theory of matter 

 for a time held out spurred him to eager mathematical investiga- 

 tions. The memoir on Vortex Motion, read first in April 1867, was 

 undertaken, according to his own statement, " to illustrate the 

 hypothesis that space is continuously occupied by an incom- 



