ULTRAMICROSCOPES 
117 
part in the forma¬ 
tion of images, 
although the illu¬ 
minating rays in¬ 
clude a range of 
high aperture, i. i 
to 1.35. There is 
thus obtained the 
greatest brilliancy 
of image upon the 
darkest of back¬ 
grounds. 
Although many 
different ultracon¬ 
densers are obtain¬ 
able, space forbids 
a consideration of 
more than two 
types: the cardi- 
oid condenser of 
Siedentopf as made 
by Zeiss, and the 
ultracondenser of 
Jentzsch as made 
by Leitz. 
The Cardioid 
Ultramicroscope 
consists of an or¬ 
dinary compound 
microscope M, Fig. 
57, into whose sub¬ 
stage ring the car¬ 
dioid condenser C 
is introduced and 
held in place by 
the clamping screw 
t. A thin film of 
Fig. 57 - The Cardioid Ultramicroscope. 
