98 Prof. Forbes's Researches on Heat. 



the gradual abandonment of such doubts, and the entire 

 adoption of my conclusions. 



I believe that only a single exception remains to this state- 

 ment. I expressed my belief in my Jirst paper that heat was 

 differently polarizable, according to the source whence it was 

 derived. M. Melloni* failed to verify this result, and the 

 opposite conclusion, namely, that all kinds of heat are equally 

 polarized by a given pile of mica, was prominently put forth 

 by himself and M. Biot as an important discoveryf. With- 

 out any undue confidence in my first, confessedly imperfect, 

 researches, I proceeded in my second paper :j; to give what 

 I considered ample proofs of the correctness of the state- 

 ment, though the great dissimilarity of the numbers arrived 

 at from those of my first paper, showed that the latter were 

 worthy of very little confidence on the ground of numerical 

 exactness, which, indeed, I never claimed for them. The 

 later experiments, however, were made with a view to accu- 

 rate results, and I stated certain forms of the experiment 

 which I had devised on purpose to meet the objections of 

 M. Melloni, although I avoided mentioning his name. 



It seems, however, that M. Melloni, returning to the subject 

 with his accustomed diligence, after receiving my second 

 paper, still confirmed his former results, and he has attempted 

 to show, in a very long paper, published in the Annales de 

 Chimie ifor May 1837 (which only appeared in October), that 

 his results must be exact, and the probable source of my 

 errors. I contented myself with giving a very brief answer 

 to this paper in the Philosophical Magazine for December 

 1837, admitting the improbabiHty that so experienced an 

 operator as M. Melloni should be wrong in his numerical re- 

 sults, but stating convincing grounds for believing that his 

 explanation of my conclusion, founded on experimental errors, 

 was inapplicable. The inquiry which I have since been led 

 to make, and the entirely satisfactory explanation at which I 

 have arrived of a difference so puzzling, terminating in a con- 

 firmation of my original statement, I now proceed to detail. 



I have not the remotest intention of examining and critici- 

 sing M. Melloni's paper in the Annales de Chimie for May 

 1837} as respects trifling or personal matters, which I readily 

 confide to the impartiality of those best qualified to judge : 

 but it is quite necessary to state the facts which I had ob- 

 served, and M. Melloni's mode of accounting for them. 



With two polarizing mica bundles of great tenuity, pre- 



* Comptes Rendus de PAcademte des Sdeiwes, ii. 140. f Ibid. p. 194. 

 X Lond. and Edinb. Phil. Mag., vol. xii. p. 549 et teq. 



