XI. AVHEN TO USE SPECIAL MICROSCOPES 371 



K. INACCESSIBLE SPECIMENS AND SPECIALIZED 



MICROSCOPES 



The laboratory type and the more generally used special micro- 

 scopes have been described. There are other kinds that should be 

 mentioned with reference to their adaptations to special problems. 

 Folding pocket microscopes, for example, are convenient for field 

 work and vary in size and equipment from a simple pocket instru- 

 ment of limited magnification to folding microscopes with a nose- 

 piece and three objectives that fit into small carrying cases. 



Many kinds of microscopes have been built for such special uses 

 as the observation of the interior of body cavities. Some endoscopic 

 instruments with low magnifying power have prisms for seeing around 

 corners, e.g., gastroscopes, laryngoscopes, etc. Capillary micro- 

 scopes are used to examine changes in the capillaries of the finger 

 (65,68) . A cathetometer consists of a microscope mounted on a ver- 

 tical moving member and provided with a scale and vernier for meas- 

 uring small distances, e.g., of growing organisms (11a). Other 

 mountings move the microscope body horizontally and are used for 

 measuring spectrograms, verifying scales, and measuring short dis- 

 tances (64)- Some microscopes have elaborate, calibrated stage 

 mechanisms for holding specimens and turning them for the measure- 

 ment of angles or distances as in the Toolmaker microscope (64)- 

 Universal microscopes include built-in light sources and various 

 special microscope bodies may be used on them interchangeably 

 (65,68). 



Microprojectors consist of a microscope and light source for pro- 

 jecting the image onto a screen. The smaller ones have tungsten 

 lights and the larger ones are provided with intense carbon or mercury 

 arcs. Industrial microprojectors usually have a self-contained screen 

 and may have scales for use on the image as in contour projectors. 



For work at high magnification it is necessary to design the equip- 

 ment for freedom from vibration and it is desirable to have better 

 control with slower focusing motions. Notable designs for horizon- 

 tal microscopes have been described by Lucas (44) and by Graton 

 and Dane (45). Harvey (46) designed a combined centrifuge and 

 microscope to observe the specimen during centrifugation. 



