564 PROFESSOR WILLIAM THOMSON'S ACCOUNT OF 



Appendiic. 



(Read April 30, 1849.) 



41. In p. 30, some conclusions drawn by Carnot from his general reasoning 

 were noticed ; according to which it appears, that if the value of /j. for any 

 temperature is known, certain information may be derived with reference to the 

 saturated vapour of any liquid whatever, and, with reference to any gaseous mass, 

 without the necessity of experimenting upon the specific medium considered. 

 Nothing in the whole range of Natural Philosophy is more remarkable than the 

 establishment of general laws by such a process of reasoning. We have seen, 

 however, that doubt may exist with reference to the truth of the axiom on 

 which the entire theory is founded, and it therefore becomes more than a matter 

 of mere curiosity to put the inferences deduced from it to the test of experience. 

 The importance of doing so was clearly appreciated l)y Carnot ; and, with such 

 data as he had from the researches of various experimenters, he tried his con- 

 clusions. Some very remarkable propositions which he derives from his Theory, 

 coincide with Dulong and Petit's subsequently-discovered experimental laws with 

 reference to the heat developed by the compression of a gas ; and the experimen- 

 tal verification is therefore in this case (so far as its accuracy could be depended 

 upon) decisive. In other respects, the data from experiment were insufficient, 

 although, so far as they were available as tests, they were confirmatory of the 

 theory. 



42. The recent researches of Regnault add immensely to the experimental 

 data available for this object, by giving us the means of determining with consi- 

 derable accuracy the values of ju within a very wide range of temperature, and so 

 affording a trustworthy standard for the comparison of isolated results at different 

 temperatures, derived from observations in various branches of physical science. 



In the first section of this Appendix the Theory is tested, and shewn to 

 be confirmed by the comparison of the values of /^ found above, with those 

 obtained by Carnot and Clapeyron from the observations of various experi- 

 menters on air, and the vapours of different liquids. In the second and third 

 sections some striking confirmations of the theory arising from observations 

 by Dulong, on the specific heat of gases, and from Mr Joule's experiments 

 on the heat developed by the compression of air, are pointed out ; and in con- 



