Royal Society. 73 



luminous matter which surroundef] it at some distance from 

 the planetary body in its centre ; this matter he supposed to 

 be of a phosphoric nature ; the length of the tail he esti- 

 mated at an average, about the -beginning of October, 

 to be above 100 niilUons of miles ; he described it as 

 very variable both in length and breadth, and as being a 

 hollow cone, emitting light on all its sides ; the inner side 

 he supposed mia;ht iikimine the planetary iiody in a manner 

 somewhat similar to that in which the ring does Saturn. The 

 planet which he discovered in the place of its nucleus, he 

 conclude^, shines with its ov.'n light, and not with one bor- 

 rowed fron) the sun. His chief reason for this conclusion, 

 was the extensive dark space which intervened between the 

 cometary envelope and the planetary body. From the great 

 alterations which took place in the nature and dimensions 

 of the tail, he was inclined to conjecture that comets may 

 be formed of nebuloe, that those nebulae undergo conden- 

 sation in their approach to our sun, or to some of what are 

 called the fixed stars, and that in process of tune they may 

 become regular planets. On contrasiing the appearance of 

 the late comet with that of 1807, he was inclined to sup- 

 pose ll>at of 1811 a much vounger comet than the fornier. 



Jan. 23. A paper by Mr. Campion (communicated by 

 Mr. Davy) was read, on the structure of the eyes both of 

 man and birds, particularly in relation to that faculty of 

 the eye which enables it to adjust its focus to the distance 

 of the object. The author examined the dift'erent conjec- 

 tures and theories which liave been proposed to account 

 for the circumstance, and explain how the eve can have 

 peri'ect images of objects at very different distances. It has 

 been generallv aereed, that the eye must have some con- 

 tractile power; but the existence of any organ capable of 

 such a function has never been ascertained. Mr. C. in ex- 

 amining the eyes of an eagle, was led to discover the ex- 

 istence of a small muscle attached to the sclerotica and 

 capable of contracting the eve, in a manner equal to efl'ect 

 the necessary change in tlie focal distance. The same organ 

 he discovered in some other birds, and hence he inferred 

 that something analogous exists in the human eye. He 

 observed, that images pass before the eyes of maniacs as 

 vividly and disMnctly without any sensible objects, as they 

 do over those of some persons from objects within the 

 focal distance of their eyes. 



A paper by Count Rumford was also read, on the na- 

 ture of light. The Count, firmly persuaded that ii is of 

 great commercial importance to increase the (juatitity of 



light 



