STUDIES IN GELS 



117 



constructed an electron microscope with a cold cathode. The electron 

 ravs emitted are focused bv a condenser coil and directed towards the 

 object (Fig. 79). An object coil behind the object projects a real mag- 

 nified image of the object, 

 in the same way as an object coid Cothode~^{~~Z^^^^ Light Source 



lens in the ordinary micro- 

 scope. In analogy to projec- 

 tion microscopy, this real 

 image is magnified again Obiect Airlo ck^ 

 and projected onto a screen ^~ 



\ii 



Illuminating Optic 



\r:\l^^^^^^J)=p\ Objective 



High Tension 

 Supply 



High Voltage f 

 Unit 40-60 kV L» 



TT 



Projective Lens I 



Final Image ^ 

 {Drying Agents 



A 



by a projection coil, com- 

 parable to the ocular. Since 

 electron rays are not visible, 

 a fluorescent screen is used, 

 which lights up in propor- 

 tion to the intensity of the 

 incident irradiation, thus 

 giving rise to a visible image 

 Since photographic plates 

 are not only sensitive to 

 ultraviolet and X-rays, but 

 also to electron rays, the 

 fluorescent screen may be 

 replaced by a cassette for 

 plates if microphotographs 

 are to be taken. 



The whole path of the rays must lie in vacuo, which is maintained 

 by means of vacuum pumps. For this reason the objects must be in- 

 troduced from the atmosphere into the evacuated apparatus through 

 an air lock. The electron image on the fluorescent screen is observed 

 through a window at the side. As in a projection-drawing microscope, 

 the source of the rays is in the upper part of the apparatus, the object 

 being irradiated from above, giving a projected image at about the 

 height of the table. Fig. 79 gives a comparison with the ordinary 

 microscope according to Induni's description (1945). 



So long as the objects investigated have a thickness of more than 

 0.1 fi, the image in the electron microscope is formed in the manner 

 of shadow images. Objects of considerably less thickness (order of 



Recording Device 



Fig. 79. Comparison between light microscope 



(at right) and electron microscope (at left) (from 



Induni, 1945). 



