64 PHOTO-MICROGRAPHS. 
tion is made by means of a pyramidal-shaped 
bellows, which is suspended in the same manner 
as the camera is, and is joined to it by its larger 
extremity. A less expensive coupling may be sub- 
stituted for this, and indeed any ingenious person 
will easily manage this matter by means of oblong 
or conical sections of tin or pasteboard blackened 
on the inside. 
This placing a camera within a darkened room 
may seem an unnecessary precaution; but the 
slightest leakage of light through the plate-holder 
or the camera-box and connections would be a 
serious matter in such long exposures as are re- 
quired when no heliostat is used. 
In the apparatus recommended for use in a 
room not darkened (Section IV.), a box was to be 
placed over the microscope before making the 
exposure, to prevent diffused light from entering 
the objective in front of the stage. This will 
not be necessary when the room is darkened, 
and when the exposures are short, with low 
powers. And if the operator has no occasion 
to leave the room during an exposure, the light- 
proof coupling between the screen and the micro- 
scope may be dispensed with. 
