367 



fectly free from these faults, although each negative is the repre- 

 sentative of a month's work and upwards of a hundred failures. 



I doubt if much better photographs of our satellite can be taken 

 by the way I have pursued. The future of lunar photography lies 

 in another direction : the image must not be received on a sensitive 

 plate and this copy submitted to an after process of magnifying. 

 Defects quite imperceptible to the naked eye on the small negatives, 

 are expanded into great blotches when magnified. In fact, upwards 

 of a dozen seemingly equally good negatives with which I started, 

 have, with but one or two exceptions, shown spots when enlarged. 



The magnifying must be conducted simultaneously with the pho- 

 tographing, either by having the eyepiece on the telescope, or better 

 still, by having a proper arrangement of lenses to throw a magnified 

 moon image at once on the collodion. The difficulty of want of 

 light could not be any objection, as supposing the enlarged image 

 to be equal to those which I have now taken, that would be an 

 increase of area of about twenty times, consequently 20 x 6 seconds, 

 or 2 minutes, would represent the average time of exposure ; a pe- 

 riod which, even were it prolonged four or five times, would not then 

 be too severe a tax upon a steady and skilful hand and eye. 



Description of the Photographic Process. 



The glass employed for taking the original negative of the moon, 

 was that known as " extra white colour patent plate," that for the 

 intermediate positives and large negatives was ordinary patent plate. 

 Cleaning the surface, which is an operation of especial importance, 

 was effected in the following manner. 



The glasses were dipped into and then well rubbed over with a hot 

 solution of caustic potassa ; then, after washing with water, they were 

 transferred to hot nitric acid (one part strong acid to three of water), 

 where they were allowed to remain for about half an hour. 



A piece of soft wash-leather was plentifully rinsed, first in a warm 

 dilute solution of carbonate of soda, afterwards in clean water, and 

 then well wrung until all the superfluous water was squeezed out. 

 The glass plates were taken from the nitric acid and rinsed in abun- 

 dance of clean water, and then rubbed well on every part with the 

 damp leather. This removed most of the superficial moisture ; and 

 the final drying was effected by means of another piece of wash- 



