COMPOUND MICROSCOPES 1h 
special advantage for micro-photography. Otherwise in its 
mechanical equipment it resembles very closely the medium- 
sized research microscope stand, with the exception that the 
stand is larger in its design, therefore offering universal applica- 
tion. In regard to the illuminating apparatus, it is advisable 
to mention that the one in the large research microscope stand 
is furnished with a three-lens condenser of a numerical aperture 
of 1.40, while the medium-sized research stand is provided with 
a two-lens condenser of a numerical aperture of 1.20. The 
stage of the microscope is provided with a cross motion—the 
backward and forward motion of the preparation is secured by 
rack and pinion, while the side motion 
is controlled by a micrometric worm 
screw. In cases where large prepa- 
rations are to be photographed, the 
draw-tube with ocular and the slider ' 
in which the draw-tubes glide are “Even | 
WETZLAR 
removed to allow the full aperture eT 
of wide-angle objectives to be made 
use of. 
BINOCULAR MICROSCOPE 
The Greenough binocular micro- 
Scope, as shown in Fig. 19, consists 
of a microscope stage with two tubes 
mounted side by side and moving on 
the same rack and pinion for the 
focusing adjustment. Either tube 
can be used without the other. The 
oculars are capable of more or less 
separation to suit the eyes of different Y 
observers. In each of the drub-like Rie eeeccnaueh 
mountings, near the point where the Binocular Microscope 
oculars are introduced, porro-prisms 
have been placed, which erect the image. This microscope 
gives most perfect stereoscopic images, which are erect instead 
of inverted, as in the monocular compound microscopes. The 
Greenough binocular microscope is especially adapted for dis- 
section and for studying objects of considerable thickness. 
