114 THE LIFE OF JAMES D. FORBES. [CHAP. 



' But what I principally write abdut is to tell you that 

 I have proved to demonstration, by its means, the pola- 

 rization of non-luminous heat, and have now to look to 

 further anxious results connected with it. So that I 

 consider the question for the first time decided. . . .' 



To M. QUETELET, Brussels. 



'EDINBURGH, December 5th, 1834. 



'. . . I have recently been experimenting with Melloni's 

 Thermo-multiplier, and have been much delighted with 

 it. Very lately I have been enabled to establish beyond 

 a doubt the polarization of non-luminous heat; and have 

 verified Melloni's experiment of the refraction of the 

 heat of boiling water. 



' To-day I commenced a register with a particular view 

 to you. I have got an apparatus for weighing and 

 measuring men, and shall collect annually as many 

 results from the students of my class as possible, and 

 also their strength by Kegnier's Dynamometer. I dis- 

 tinguish their age and native country. . . . Amongst my 

 many other pursuits, as I mean to begin on optics this 

 winter, I have been studying the undulatory theory with 

 great admiration. We are, I am sure, much indebted to 

 you for putting Herschel's Treatise on Light into a more 

 convenient form than we can find it in England/ 



To PROFESSOR AIRY, Cambridge. 



'EDINBUBGH, December \\th, 1834. 

 ' I have at length found leisure to read with great 

 attention, and consequently with very great pleasure, 

 your undulatory tract, which quite fulfils my expectation 

 as to the nature and extent of the evidence on this 

 marvellous subject. I have been getting sundry pieces 

 of apparatus made, and can now profit by your valuable 

 practical lessons, as well as by the papers with which you 

 have from time to time favoured me, and which I am 

 now better prepared to appreciate. Allow me to ask 

 you a few practical questions. ... I hope you will not 



