79 
and as no camera box is required I need not enter into any 
supposition as to the mode in which it may be done. Before 
deciding what was necessary to be done, it occurred to me 
that the telescope tube itself is the camera, and all that was 
required was the means of fixing the dark frame or plate 
holder. If the telescope be pointed to the moon, the eye 
piece removed, and a piece of ground glass held between the 
eye and the aperture, the image will be seen on the glass, and 
we require then the means of holding the sensitive plate 
steadily near the same place. All that is needed is a brass 
tube about four or five inches long, of the size exactly fitting 
the tubo of the telescope in the place of the eyepiece. In 
some cases the sliding tube of the eyepiece may be unscrewed 
and used for this purpose. At one end of this tube a thread 
is cut and is made to screw into a pipce of metal plate (in the 
centre of which is a circular aperture of the same size as the 
tube), of the same dimensions as the dark frame. Attached 
to the plate holder are clips accurately fitting the brass plate, 
but so that the frame will easly slide off and on without dis- 
turbing the telescope. This is all the additional apparatus 
required to enable photographs of the moon or any other 
celestial object to be made. A separate frame for the ground 
glass is not necessary : it must be cut to fit the dark frame, 
and while in use can be held by slight springs fixed inside 
the frame at the sides. 
The accompanying photo-lithographed copy of a drawing 
shows the arrangement of the apparatus when in its place for 
taking a negative, and renders further description unneces- 
sary. '1 he method for ascertaining the actinic focus may be 
stated in a few words. With the rack motion adjust the 
focus for distinct vision on the ground glass, and then mark 
ithe tube E, and also the sliding part of the telescope. Al- 
though very unlikely to be of the slightest use, unless taken 
with a reflecting telescope, a picture may now be taken; it 
will at least serve to give some idea of the proper exposure. 
