192 J, J. Woodward on Photo-micrography. 
The principles involved in obtaining successful photographs 
with the microscope are the following: 
1. 'To use objectives so corrected as to bring the actinic ray 
to a focus. 
2. To illuminate by direct sunlight passed through a solution 
of ammonio-sulphate of copper, which excludes practically all 
but the actinic extremity of the spectrum. 
3. Where it is desired to increase the power of any objective, 
to use a properly constructed achromatic concave instead of an 
eye-piece. 
4. To focus on plate glass with a focusing glass, instead of 
ground glass. 
5. With high powers to use a heliostat to preserve steady 
illumination. 
. Where an object exhibits interference phenomena when 
illuminated with parallel rays, as is the case with certain diatoms 
and many of the soft tissues, to produce a proper diffusion of 
the rays by interposition of one or more plates of ground glass 
in the illuminating pencil. 
Strict adherence to these principles is indispensable to success. 
= he Museum they have been carried out by the following 
etails : 
occupied by a shutter about fourteen inches high on which the 
blackened sash shuts down light-tight. In this shutter is a 
phragm or the achromatic condenser fits into the tube projecting 
inward from the shutter by which the sun’s light reflected from 
the mirror outside is admitted. A black velvet hood covers the 
rts about the stage and objective of the microscope, and thus 
prevents the leakage of light into the room. 
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