46 
PRACTICAL PHOTO-MICROGRAPHY. 
box—quite a convenient arrangement—the door is then 
closed, and attention is directed as usual to the ground- 
glass. Of course with this arrangement the plane 
mirror is used, and such radiant and paralleliser as may 
be desired. 
The rest of the device for the double purpose of 
watching the object up to some desired juncture and 
then instantly making the exposure is not really com¬ 
plicated. Inside the box on a shelf is placed a flat 
piece of wood (fig. 14), with an aperture corresponding 
to the tube of the microscope, and across this aperture 
passes a plate with two similar apertures, one of which, 
by the way, is variable in size at will of the operator. 
At an angle of 45 degrees to the non-variable aperture 
is a very thin and true mirror u, which reflects the 
image into the brass tube T (fig. 13), seen projecting 
from the side of the box. The sliding plate carrying 
mirror and apertures is actuated by a barrel spring b, 
and has simple and common arrangements for setting, 
releasing, and giving “ time ” exposures at will. The 
brass tube of course has ground-glass at its end, and is 
made to telescope, for the distance from the ground- 
glass let into the external end of this tube must be the 
same distance from the mirror as the mirror is from the 
ground-glass of the camera proper. In practice, having 
arranged our object and its illumination and other 
details as desired with our head in the box, the shutter 
is set, the shutter arrangement covered, except for a 
hole in the axis, the box locked, the plate inserted, and 
the shutter of the dark slide drawn, we take our seat at 
