110 



SCIENTIFIC THOUGHT. 



philosophical speculations which tended to prevent 

 their ready acceptance, it cannot be denied that, as 

 a first approximation, " his equivalent " was sufficiently 

 near the truth to be practically useful. 



But neither the happy generalisation of Mohr, which 

 was lost or forgotten, nor the numerical estimate of 

 Mayer, which remained unnoticed, succeeded in impress- 

 ing contemporary philosophers with the importance of 

 the subject. This was done almost at the same date, 

 though quite independently, by the persistent and per- 

 severing experiments and measurements of James Pres- 

 cott Joule, who laboured unnoticed and practically 

 without support from 1841 to 1847, when he had 

 the good fortune of gaining the attention and friend- 

 ship of William Thomson (Lord Kelvin). 1 



1 Joule not only defined more 

 clearly the different data and con- 

 ditions on which the correctness of 

 the result must depend, but had 

 also at his command a much greater 

 wealth of novel experimental facts, 

 brought together by his own re- 

 sourceful mind. Thus from 1843 

 to 1850 he published no fewer than 

 ten series of experiments, approxi- 

 mating from widely differing results 

 to the true figure. See Helm's list 

 (' Energetik,' p. 34). After he had 

 laboured for more than five years 

 his work was, in 1847, at the meeting 

 of the British Association in Oxford, 

 still almost unknown. He himself 

 reports as follows in 1885 ('Joint 

 Scientific Papers,' 1887, p. 215): 

 " It was in the year 1843 that I 

 read a paper ' On the Calorific 

 Effects of Magneto-Electricity and 

 the Mechanical Value of Heat ' to 

 the Chemical Section of the British 

 Association at Cork. With the ex- 

 ception of some eminent men . . . 



the subject did not excite much 

 general attention ; so that when I 

 brought it forward again at the 

 meeting in 1847 the chairman sug- 

 gested that, as the business of the 

 section pressed, I should not read 

 any paper, but confine myself to a 

 short verbal description of my ex- 

 periments. This I endeavoured to 

 do, and discussion not being in- 

 vited, the communication would 

 have passed without comment if a 

 young man had not risen in the 

 section, and by his intelligent ob- 

 servations created a lively interest 

 in the new theory. The young man 

 was William Thomson, who had two 

 years previously passed the Univer- 

 sity of Cambridge with the highest 

 honour, and is now probably the 

 foremost scientific authority of the 

 age." See also Lord Kelvin's ac- 

 count of the meeting in 1847 in 

 ' Popular Lectures and Addresses ' 

 (London, 1894, vol. ii. p. 556, &c.) 



