120 THE LIFE OF JAMES 1). FORBES. [CHAP. 



to our Royal Society about Auvergne, and particularly 

 upon elevation craters, which was <|uite in point. I am 

 writing a paper just now which T intend for the R. S., 

 London, on the Pyrenean springs, their temperature, 

 geological relations, &c. ; and on the former point, temp., 

 I am vain enough to hope that it may prove a sort of 

 model to future observers : at least no one has hitherto 

 so observed, I believe. I have also in hand a little 

 Gothico-mathematical speculation which perhaps you 

 may laugh at ; but I give you leave beforehand. 



* But these are only secondary occupations, which, with 

 my lecturing labours, only revolve round my primary, 

 the polarized heat. I have managed to magnify the 

 effects so as to be, I hope, beyond cavil. ... I think 

 that experiment is a quietus for Biot. . . . Excuse this 

 very long story, and pray come down and see my experi- 

 ments. When I have finished what I am doing I should 

 be most happy to look into your conductivity. ... If 

 Mr. Airy is with you, pray give him the above numerical 

 results.' 



On February 2nd, 1836, we find him writing thus to 

 Dr. Whewell on the first blush of a new discovery he had 

 just made : 



' EDINBURGH, Feb. 2nd, 1836. 



' I cannot help writing two lines in a hurry to tell you 

 that I succeeded yesterday in making the most curious 

 discovery respecting heat, it seems to me, that I have 

 yet arrived at, and one quite decisive of the identity of 

 its character with that of light. I found that dark heat is 

 copiously reflected within rock salt at an angle too great 

 for its emergence. This I had foreseen last summer 

 before I was aware that Melloni had actually tried it, 

 and at the same time I conceived the possibility of 

 trying whether two total reflections would produce the 

 same effect in the case of heat as in that of light. I 

 have had a Fresnel's rhomb made of rock salt with 

 angles of 45 one of the critical ones, nearly, calculated 

 by this formula, giving //, its proper value for light. I 



