152 PROPAGATION OF JOULE'S VIEWS. 



resistance. This was comparatively a simple matter, and 

 he was in no way responsible for the mechanical value 

 assigned to the electric action as measured by the British 

 Association unit of resistance ; the value of which unit was 

 determined by others. Joule accomplished his part with 

 his usual skill and accuracy, devising an absolute current 

 meter for the purpose. Then, dividing the mechanical 

 value of the electric action (obtained by the B.A. unit) 

 by the heat, he obtained 782 lbs., which, although about one 

 per cent, larger than the value obtained with water, was a 

 splendid verification of the electric measurements. Never- 

 theless the discrepancy, until it was explained, cast a 

 possibility of doubt on the 772 lbs. 



After the mathematical development of the general 

 theory of thermo-dynamics had been completed by Thomson, 

 Rankine, and Clausius, in 1855, the interest in the subject 

 was not allowed to lapse, but was rather enhanced by the 

 less general direction which was given to it, in the develop- 

 ment of the dynamical theories of gases by Clausius, and 

 of electricity by Thomson and Helmholtz, whose work was 

 so ably taken up by C. Maxwell and P. G. Tait and 

 Boltzman, and secured the attention of all the leading 

 physicists of the time. 



Rankine's Manual on " The Steam Engine," published 

 in 1 860, and already in I S6S at the end of the third edition, 

 had brought the practical importance of the new theory 

 before the engineering profession, pointing out clearly and 

 definitely the economic possibilities, as well as the advances 

 in mechanical construction necessary for this realisation. 



At the same time Hirn had lent his powerful aid 

 to propagate Joule's views and the new theory on the 

 Continent. In 1865, Hirn repeated Joule's experiments for 



