ULTRAAI ICROSCOPES 



125 



an adjustable slit-diaphragm, thus permitting the cutting down 

 of the field until only a certain selected portion is visible. 



The mutual arrangement of the two objectives is shown in 



Fig. 6i. Zsigmondy Immersion Ultramicroscope. 



the diagram. These objectives embody several unique ideas in 

 mounting, construction and in the component lenses themselves; 

 the end, or front, lenses are of quartz. An examination of the 

 diagram will show that a drop of liquid brought into contact 



