vi.J PROFESSORIAL LIFE. 129 



total effect. I think you have not mentioned total re- 

 flection and circular polarization. 



1 As to simple reflection, Melloni should be mentioned 

 alone, but I claim double refraction/ 



The following extract from a letter to Professor Airy 

 shows what his occupations were, and how closely his 

 lectures and researches were combined : 



To G. B. AIRY, ESQ. 



' THE DEAN HOUSE, March 15, 1837. 



* I have been exceedingly busy, and not very well, 

 which have been the causes of my silence. Amongst 

 other occupations 1 have had to read five essays, which 

 I have received in competition for a medal I proposed, 

 on the Undulatory Theory of Light, a new subject in 

 Scotland, which I am delighted to find has stirred up our 

 youth, and I have got some really respectable composi- 

 tions. This is a proof to me that things arc mending, 

 and that exertion, private and personal, is not thrown 

 away, <j\vn where public sympathy or support is not to 

 be looked for. 



'I have not abandoned my polarized heat, but have 

 been much driven about this winter. I have got twelve' 

 inomcters sunk in different soils from three to twenty - 

 >ix feet ire conduction. Shall you be eer- 



ily at Given wich the last days of April ? ' 



The following letter, written about this time, proves 

 that the intercourse with Sir David Biv \vstn-, for a time 

 suspended, was now cordially renewed : 



>IR DAVID, 'EDINBURGH, April 28(h, 1837. 



'. . . . Your ex]H-i-ini( nis on absorption must be 



[ think Wrede, the first pages of whose 



/ bas lat<-!y translated, has done something 



;! kind y<>u allude to, if 1 un<l-i>tand it con < -tly. 



If I ivrolh'1-t well. In- imitates the phenomena of absorp- 



ly rnmltin, (' thin mi-a plates that i<, by tlio, 



colour- "f thin |la: 



