280 Geological Society : — 



(2) The galvanometer received the fire-fly radiation through 

 a lens which occupied 0*00655 of a hemisphere, and would 

 have transmited this fraction of the total heat except for its 

 position, which caused it to transmit J more than the average, 

 which is 0*00873 (g). The measured radiation from this 



fractional part gave 0*84 div. (h), and - =96*2 div. is the 



deflexion which would be given by the total abdominal 

 emission, or 



96*2 x 0*000000684 = 0*0000658 cal. 



Since the luminous surface has an area of about ^ square 

 centim., this corresponds to a radiation of 0*00039 per square 

 centim. of radiating surface in the time of the galvanometer- 

 needle's swing, or to — j — = 0*0024 cal. per square centim. 

 per minute. * 



(Taking the water-equivalent of the bulb of an ordinary 

 mercurial thermometer 1 centim. in diameter at 0*25 gr., we 



fiDd 0-84 x -000000684 _ 0O . Q00002 ^ 



U* Zu 



showing that if such a thermometer were placed in the position 

 occupied by the bolometer, its rise during the time of the 

 latter's exposure to the radiation of the insect would be between 

 two and three one-millionths of a Centigrade degree.) 



XXXII. Proceedings of Learned Societies, 



GEOLOGICAL SOCIETY. 



[Continued from p. 200.] 



June 18, 1890.— Dr. A. Geikie, F.R.S., President, 

 in the Chair. 



HPHE following communications were read : — 



-*- 1. " The Borrowdale Plumbago, its Mode of Occurrence and 

 probable Origin." By J. Postlethwaite, Esq., F.G.S. 



After giving details of the mode of occurrence of the plumbago of 

 Borrowdale in veins traversing diabase and diorite, which break 

 through the Volcanic Series of Borrowdale, the author refers to the 

 modes of occurrence of plumbago in other regions, and contrasts these 

 with the surroundings of the Lake-District masses. He points out 

 that many thousand feet of volcanic rock supervened between the 

 Borrowdale plumbago-bearing rocks and the overlying carbonaceous 

 shales of Silurian age. On the other hand, he finds similarities 

 between the containing rocks in Borrowdale and the diamond- 



