ARRANGEMENT OF MICROSCOPE AND CAMERA. 51] 
The microscope must be fastened to the board 
in a firm and substantial manner, but in such a 
way that it may readily be detached; for this 
arrangement does not conveniently admit of the 
application of the eye to the eye-piece of the mi- 
croscope for the purpose of searching a suitable 
field and focusing. It will therefore be found 
convenient in practice to detach the microscope 
for this purpose, and to place it in position on the 
board when a field has been selected. For this 
reason, the attachment should be by a clamp which 
can be quickly fastened, and that without inter- 
fering with the adjustment. 
The connection between the camera and the 
microscope must be light-proof. 
The operator will not be able to reach the ad- 
justment screws for the purpose of focusing upon 
the screen when the bellows of the camera are 
extended to the full length, and the following 
expedient, therefore, is recommended to meet this 
difficulty : — 
A drum of wood or metal two or three inches 
in diameter and half an inch thick is attached to 
the milled head of the coarse adjustment on one 
side of the instrument. This has raised margins, 
and serves to carry a cord which passes around it 
with one or two turns. One extremity of this 
cord passes through a hole in the board to which 
the instrument is attached, and supports a weight. 
The other extremity also passes through a hole in 
the support and around a pulley which changes 
its direction towards the screen end of the appa- 
