118 THE LIFE OF JAMES D. FORBES. [CITAP. 



The summer of 1835 was spent abroad, and therefore 

 falls to be noticed in another chapter. On his return to 

 England after a visit to Fettercairn, he thus writes from 

 Edinburgh to Sir John Herschel, who was then engaged 

 in scientific observations at the Cape of Good Hope : 



' EDINBURGH, October 25th, 1835. 



'The results of your table appear to me very satis- 

 factory and interesting. One thing strikes me as requir- 

 ing new investigation, viz., what are really the hours 

 of maxima and minima, which in your fine climate 

 might be easily fixed ; for I have no doubt that the 

 diurnal curve is very different from ours. I argue this 

 rom the circumstance that the barometric pressure at 

 noon, instead of being the mean of the day, coincides 

 very nearly in your table with that of 9 A.M., which 

 therefore in all probability is not the hour of maximum. 



1 1 assumed the hourly variation to be a function of the 

 latitude, simply because the tables of observation seem 

 to indicate it ; and, whatever may be the true theory, it 

 does not seem to me that the mere distribution of sea 

 and land can be regarded as the main cause of the 

 y;t nation. In conformity with your wish, conveyed by 

 Mr. Who .well, I endeavoured to get observations es- 

 tablished at Malta ; and wrote to Dr. Davy for the 

 purpose. ... He has returned, however, to England, but 

 I will try to get new ones set on foot here at the College. 

 The formula given by me was empirical. . . . The Asso- 

 ciation is itself the best Meteorological Society that ever 

 was formed, and capable of doing almost anything. ... 1 

 have been led to study the undulatory theory, particularly 

 lately in reference to my own inquiries and lectures, and 

 have received from it the same pleasure which everyone 

 must do who approaches the subject with perseverance 

 and candour. ... I have exhibited all the chief 

 phenomena of polarization upon screens on the large 

 scale to my class, for the first time in Scotland. You 

 must have heard so much about the comet, that I need not 

 add my account of it. It has really been a fine object/ 



