rilOTOMlCROGK.-IPHV .1X1) TI.CIIXIC.II. MlCROSCOl'V 121 



One of these illiimitiating trains functions with a microscope which 

 has mounted on its objective a clamping device for holding Biltz 

 cells in which the iitjuids are placed for examination. The other 

 train serves another microscopn; on the stage of which is mounted a 

 siH-cia! object stage capable of being raised and lowered and provided 



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 11 



Fig. 21 — Illustrating clifTraotion of light impinging upon an ultra-microscopic particle. 

 Illuminating rays represented by solid lines and diffracted rays by dotted lines. 



with a plate at the top to receive the specimen to be examined. In 

 this case the specimen, if a hard solid, has been previously prepared 

 to have two ground and polished surfaces in planes at right angles to 

 each other and is mounted so that one faces the illuminating train 

 and the other the objective of the viewing microscope. Plastic 

 substances or certain liquids not suited to the use of the Biltz cells 

 are placed in a special glass cell having a deep cylindrical recess 

 faced with a quartz window toward the illuminating train. Various 

 cells for ultra-microscopic examinations are shown in Fig. 22. 



Placed next to the arc lamp is a fixtxl diaphragm and then a small 

 projection lens which is corrected chromatically and spherically and 

 brings the image of the positi\e carbon of the arc lamp to a focus on 

 the adjustable slit. The slit is provided with a drum bearing a scale. 

 The divisions of the scale embrace 50 parts and a complete revolution 

 of the drum opens the slit ,'j mm. so that each division of the scale 

 advances the slit l/lOO mm. The slit is fitted with two jaws at right 



