28 PHOTO-MICROGRAPHS. 
sky, —the rays are practically parallel, and the 
complications are avoided which are introduced 
when a reflecting surface or refracting lens is 
interposed. 
For higher powers, and after learning how to 
make good negatives with the simplest conditions 
possible, the student may place an achromatic 
condenser beneath the stage. An achromatic 
object-glass may be used for this purpose. The 
sub-stage of the microscope should be arranged to 
carry any objective having the Society’s screw, 
and to enable the operator to adjust this at the 
proper distance from the object. This distance 
will depend upon the power of the condensing 
lens, and also upon that of the objective employed 
in front of the object to project the image. 
When a condensing lens is used, it should be 
adjusted by trial to that point which gives the 
best definition to an object properly focused on 
the screen. If it be brought nearer to the object 
than this most favorable point, the illumination 
of the field upon the screen will be brighter, and 
the image may for this reason appear more dis- 
tinct. But a careful inspection will show that 
there is loss of definition, and that the finer details 
of the projected image are obscured or entirely 
lost. This will be still more apparent in a nega- 
tive made under these circumstances. 
If the light is insufficient when the condenser 
is adjusted to the best point for definition, it will 
be necessary to place another condensing lens of 
larger diameter —a bull’s-eye condenser may be 
