Electric Lights for Photo-micrography. 299 
sees at a glance how the object will appear in the photograph 
(in which the same black lines or tints will be faithfully repro- 
uced on a white field) and is thus enabled to arrange his 
achromatic condenser and other adjustments so as to produce 
the most satisfactory effect. 
Every thing having been arranged at the microscope to the 
satisfaction of the observer, the eyepiece is taken out, and the 
image allowed to fall on the ground glass of the plate holder, 
which has previously been placed at the distance necess 
give the magnifying power desired with the objective employed. 
The operator adjusts the plate holder to the right height and 
sees that it is perpendicular to the optical axis of the microscope, 
which he readily does by observing that all parts of the field 
are equally in focus. He then takes out the ground glass and 
inishes the fine adjustment with a sheet of plate glass and a 
focussing glass, after which the sensitive em is inserted, the 
at a distance from it at the sensitive —_ the following con- 
trivance is employed. On the table w! 
joint of an ordinary fishing rod, to w 
like a watch key, has been rivetted, enables the operator to 
e 
not differ in any r t from those used in ordinary pho 
graphic work, te I ae found that by employing a practical 
lowi the dark room 
