NEW MICROSCOPES—SEIDEL AND WINTER 195 
the magnetic fields on a short section of the microscope’s axis. Whereas 
in the ordinary light microscope glass lenses serve as the refractive 
media through which light rays are deflected, in the electron microscope 
it is these magnetic fields of rotational symmetry which are the refrac- 
tive media and serve as the “lenses” which deflect the beams of 
ELECTRON 
SOURCE LIGHT SOURCE 
Th 
iF 
H \ 
MAGNETIC | CONDENSER 
CONDENSER | eels 
|| | 
MAGNETIC . OBJECTIVE 
OBJECTIVE I \\ LENS /| 
| i] \ 
/ | \ / | \ 
’ \ 
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INTERMEDIATE 
IMAGE PROJECTOR 
PROJECTOR LENS 
/ \ 
/ \ | \ 
OBSERVATION 
SECOND STAGE SCREEN 
MAGNIFIED IMAGE (PHOTOGRAPHIC PLATE) 
Figure 1.—Comparison of a simplified cross section of an electron microscope 
(left) with that of an ordinary light microscope. 
electrons. The first of these, the condenser lens coil, corresponding to 
the substage condenser of the ordinary light microscope, concentrates 
the beam of electrons upon the specimen. The convergence of the 
beam falling on the specimen is controlled by varying the current 
through this condenser lens. Now, having passed through the speci- 
men, the objective coil, similar in effect to the objective lens, focuses 
the electrons, and an intermediate image enlarged about 100 diameters 
