COMPOUND MICROSCOPES 



15 



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, tiierefore offering universal appUca- 

 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 

 removed to allow the full aperture 

 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 

 observers. In each of the drub-like 

 mountings, near the point where the 

 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. 



Fig. 19. — Greenough 

 Binocular Microscope 



