363 



February 12, 1857. 



W. R. GROVE, Esq., V.P., in the Chair. 

 The following communications were read : 



I. " On the Photography of the Moon/' By WILLIAM CROOKES, 

 Esq. Communicated by Professor STOKES, Sec. R.S. Re- 

 ceived December 16, 1856. 



The subject of lunar photography is one which has engaged the 

 attention of scientific men almost from the first announcement of the 

 possibility of fixing the images in the camera. Owing to the extreme 

 difficulty of satisfying all the conditions of the problem to be solved, 

 there are few good photographs of the moon yet in existence. It 

 was my good fortune in the autumn of 1855 to obtain several ex- 

 cellent pictures of this kind, and since these form the starting-point 

 of the work which, by the assistance of a grant from the Donation 

 Fund of the Royal Society, I have been pursuing during the greater 

 part of the last year, a detailed account of the means employed for 

 their production will not, I think, be considered out of place here. 



The telescope in which these pictures were taken is the magnifi- 

 cent equatorial at the Liverpool Observatory. This, together with 

 all the resources of the establishment, was placed at my disposal by 

 my kind friend Mr. Hartnup, to whom it is but due to state, that, 

 were it not for the invaluable assistance afforded me by his sterling 

 advice as well as steady hand, the results would not have been worth 

 keeping. 



The mounting of the equatorial is quite unique ; the polar axis and 

 telescope togetber weigh about five tons, and whilst all parts are so 

 truly and smoothly fitted that this enormous mass is moved cquato- 

 rially by means of a small water-mill with such marvellous accuracv, 



VOL. VIII. 2 F 



