70 



The Electron Microscope 



sections, can be tilted to align it with the rest. The final image 

 can be observed on a fluorescent screen just above the photo- 

 graphic plate. Exposure is effected by tilting this screen out of 

 the way. Once aligned the instrument will hold its adjustment 

 for a long time, in many repeated exposures. 



The object chamber can be seen open in figure 19. It contains 

 a moveable object stage and the object changing mechanism. 

 The stage allows moving the object in two directions at right 

 angles to one another. Models have been made also for stereo- 

 scopic photography which enable tilting the object around a 

 horizontal axis. The specimen holder is a small thimble which 

 during operation rests about 5 mm above the center of the 

 objective. It is attached to a lever system which is operated by 



Fig. 20. Photograph of rear of Type B electron microscope, showing 

 electrical supplies. The resonant circuit which produces the high voltage 

 at vi2 kc is contained in the oil tank, near the top 



