56 PHOTO-MICROGRAPHS. 
might also be used, by placing the apparatus in 
a window facing the south. 
The main advantage of this simple apparatus 
is that it is portable, and can be put aside when 
not in use, and consequently does not require 
a special room fitted up as an operating-room. 
When, however, it is practicable to devote a small 
room to the purpose, the arrangement next to be 
described possesses decided advantages. 
V. OPERATING-ROOM AND FIXTURES. 
When a room ts available for the purpose, matters are 
very much simplified by making this the camera, inside 
of which the operator works. In this case, the room 
is darkened, and no actinic light is admitted, 
except that which comes through a properly 
located aperture to the achromatic condenser, or 
directly to the object if no condenser is em- 
ployed. 
This arrangement enables the operator to stand 
directly before the microscope — fastened upon a 
support in a horizontal position — for the purpose 
of selecting a field, and then to project and focus 
the image upon the ground-glass screen. This 
has a separate support, and is not necessarily 
coupled with the microscope by a lght-proof con- 
nection. When a hehostat is to be used, the optical 
axis of the microscope must be on the meridian, 
and in a perfectly horizontal position. 
The supporting shelf should be placed in a 
