ARRANGEMENT OF MICROSCOPE AND CAMERA. 55 
many of the best homogeneous immersion objec- 
tives are unprovided with cover-correction. 
When such an apparatus as we have described 
is used in a room from which the light is not ex- 
cluded, it will be necessary to shut off the light 
from in front of the objective, with the exception 
of that portion which is required for the illumi- 
nation of the field. This is especially necessary 
when light reflected from the sky is used, and 
the time of exposure is comparatively long. A 
movable cover of wood or pasteboard blackened 
on the inside and made to fit over the micro- 
scope, may be used for this purpose. A circu- 
lar aperture at the outer end admits the light 
to the object, and this may carry a condensing 
lens, if desired, when there is an achromatic con- 
denser upon the sub-stage. If no achromatic 
condenser is used, this aperture should be very 
near the stage of the microscope, and diaphragms 
are employed to shut off all light except that 
required for the illumination of the field to be 
photographed. 
It is evident that no modification of the appara- 
tus described is required, if the intention is to use 
lamplight, except that the support should project 
in front of the microscope a sufficient distance to 
make room for the lamp. In this case, also, the 
cover intended to shut out diffused light from in 
front of the objective could be dispensed with, 
and a simple screen substituted for it, having an 
aperture at the proper level, into which the bull’s- 
eye condenser could be introduced. A heliostat 
