214 Professor Joseph Larmor [May 1, 



formations. What is perhaps now more interesting is that it expresses 

 a decided opinion (which he still retained in 1892) on a question 

 which Helmholtz * to the end preferred to leave open, namely, 

 whether the refinements of minute structure and adaptation in vital 

 organisms may permit departure from the law of dissipation, which 

 is known to be inflexible in the inorganic world, by utilising to some 

 extent diffuse thermal energy for the production of vital mechanical 

 power. The development of Clause ;-> led to the famous series of 

 investigations and discussions regarding the beginnings and the ulti- 

 mate fate of our universe, and the duration of geological time, which 

 have formed a region of intimate contact, but not always of agree- 

 ment, between dynamical and evolutionary science. 



Earher in the same note, and also more fully in 'Phil. Mag.,* 

 February 1853, Thomson illustrated his early complete grasp of all 

 matters relating to the availability of thermal energy and to compen- 

 sating transformations, in calculating the dissipation which arises from 

 throttling steam, and the work which can theoretically be gaiued from 

 the thermal energy in an unequally heated space. 



This history is, however, not yet complete. Examination of the 

 ' Notes inedites ' of Sadi Carnot, appended to the reprint of the • Re- 

 flexions,' published with charming biographical detail by his brother in 

 1878, and welcomed enthusiastically by Lord Kelvin, leaves an im- 

 pression that Carnot was already struggling Avith difficulties of the 

 kind to which the insight of Thomson exposed him some twenty years 

 later. He had analysed (p. 91), with sure instinct, the Gay-Lussac 

 experiment concerning heat of expansion of gas by efilux, and after- 

 wards developed it (p. 96) into a suggestion of the identical porous 

 plug experiment of Joule and Thomson. He points out (p. 92) that 

 the view that heat is "le resultat d'un mouvement vibratoire des 

 molecules " conforms to our knowledge in a long list of the principal 

 transformations of energy ; " mais il serait difficile de dire pourquoi, 

 dans le developpement de la puissance motrice par la chaleur, un 

 corps froid est necessaire, pourquoi, en consommant la chaleur d'un 

 corps echauffe, on ne pent pas produire du mouvement." He seems 

 to be trying (p. 94) to think out a definite distinction between this 

 movement of the particles of bodies and the " puissance motrice "into 

 which it cannot be changed back. " Si les molecules des corps ne 

 sont jamais en contact intime les unes avec les autres, quelles que 

 soient les forces qui les separent on les attirent, il ne peut jamais y 

 avoir ni production, ni perte, de puissance motrice dans la nature. 

 Alors le retablissement d'equilibre immediat du calorique et son 

 retablissement avec production de puissance motrice seraient essentielle- 

 ment differents I'un et I'autre." " La chaleur n'est autre chose que 

 la puissance motrice, ou plutot que le mouvement qui a change de 



* See an interesting passage in his Lectures on Heat, posthumously pub- 

 lished. 



