Fig. 17.—Research Microscope Fig. 18.—Special Research Microscope
SPECIAL RESEARCH MICROSCOPE
A special research microscope of the highest order (Fig. 18) is supplied with an extra large body tube, which renders it of 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 application. 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 preparations 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.
Fig. 19.—Greenough Binocular Microscope
BINOCULAR MICROSCOPE
The Greenough binocular microscope, 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 dissection and for studying objects of considerable thickness.
POLARIZATION MICROSCOPE
The polarization microscope (Fig. 20) is used chiefly for the examination of crystals and mineral sections as well as for the observation of organic bodies in polarized light. It can, however, also be used for the examination of regular biological preparations.