382 



Anniversary Meeting. 



[Nov. 30, 



plates for determining the positions of the other stars. Indeed I think 

 the practicability of this application may now be considered as esta- 

 blished, and there only remains the question of the best mode of 

 carrying it out on a uniform plan. In the course of the autumn I 

 had a letter from Admiral Mouchez, Director of the Paris Observatory, 

 in which he informed me that in response to the presentation of 

 specimens of the admirable star photographs taken by the MM. Henry, 

 several of the astronomers to whom they had been sent suggested 

 that it would be well that a conference of astronomers of various 

 nations should be held, with a view to taking concerted action for 

 obtaining on a uniform plan a complete map of the whole starry 

 heavens. He wished accordingly to obtain an expression of opinion 

 on the part of the Royal Society as to the desirableness of holding 

 such a conference ; and as it was contemplated, in case the proposal 

 should be favourably entertained by those consulted, that the con- 

 ference should be held at Paris in the spring, and it would be neces- 

 sary to give timely notice to the astronomers who live in the southern 

 hemisphere, an early reply was requested. 



As it would have defeated Admiral Mouchez's object to wait till 

 the Council should reassemble after the recess, I wrote at once to 

 consult four of our Pellows specially named by Admiral Mouchez ; and 

 on receiving their replies I wrote to Admiral Mouchez, saying that 

 under the circumstances I took it upon me to express in the name of 

 the Royal Society our approval of the suggestion, explaining at the 

 same time that I did so on the understanding, which I fully believed 

 to be in accordance with his intention, that the astronomers who 

 might attend the conference should not be considered as pledged to 

 the adoption of the methods or scale of the MM. Henry, but that the 

 whole subject should be open to discussion. On reporting what I had 

 done to the Council when they met after the recess, I obtained an 

 expression of their approval. 



In these photographs a remarkable instance was exhibited of the 

 power of photography to reveal the existence of objects wholly invi- 

 sible to the eye. One of the stars of the Pleiades was found to be 

 surrounded by a nebula which cannot be seen with telescopes. The 

 reason of the difference of power of the plate and eye is very obvious ; 

 with the eye an object is either seen or not seen at once, whereas 

 with the plate, provided there be an absence of stray light, feebleness 

 of intensity can be made up for by length of exposure. 



But the MM. Henry are by no means the only persons who have 

 applied photography to the delineation of the stars. Among others 

 our Fellow, Dr. Gill, who has sent us some excellent specimens of the 

 photographs obtained by his instrument, proposes to take at the Cape 

 Observatory photographs of the whole starry heavens of the southern 

 hemisphere, under such conditions as to include the magnitudes 



