ULTRAMICROSCOPES 67 



The Cardioid Ultramicroscope consists of an ordinary com- 

 pound microscope M, Fig. 30, into whose substage ring the 

 cardioid condenser C is introduced and held in place by the 

 clamping screw /. A thin film of the liquid to be examined is 

 contained in a special quartz cell Q which in turn is held in posi- 

 tion upon the stage in a cylindrical brass mounting B. This 

 mounting may be leveled or slightly adjusted in height with 

 respect to the condenser by means of the screws S. The objec- 

 tive O of the microscope must be specially corrected for use 

 with the quartz cell cover and must have a numerical aperture 

 of less than 0.9. This latter requirement is accomplished by 

 introducing into the objective a funnel diaphragm. As set up 

 for use, the cardioid condenser receives substantially parallel 

 rays from the microscope mirror m. The source of these rays 

 must be some powerful radiant, most conveniently an arc lamp R. 

 Parallel rays are obtained by means of a plano-convex lens L 

 mounted by means of short brass bars r, r, three in number,, 

 attached to the metal screen E. A glass cell W filled with water 

 acts as a cooling trough. A black cardboard or metal diaphragm 

 D serves to cut down the light beam to the proper size for just 

 filling the aperture of the condenser. For convenience in ad- 

 justment as to distance and height, microscope, cell and lens 



Q. o 



FIG. 31. Cell for holding Liquids for Study with the Cardioid Ultramicroscope. 



are placed upon adjustable stands with saddle base resting upon 

 an optical bench of triangular section. The screen E is tipped 

 at such an angle as to project the rays from R upon the properly 

 inclined mirror m, when the latter is at a distance of approxi- 

 mately 60 centimeters from the lens L. The crater of R should 

 be about 8 centimeters from L. 



The liquid to be studied is placed in a quartz cell Q, Fig. 31, 

 consisting of a grooved quartz disk and cover. With the cover 



