154 



INSTRUMENTATION 



the object specimen and which are partially transmitted by the highly 

 reflecting dielectric film at MGN form an image of the opening in the 

 condenser diaphragm on the conjugate area of the diffraction plate 

 after they have been reflected by the silvered portion of the surface 

 BCDE since the diffraction plate is located at the focal plane of the 

 hemispherical section. These rays are again partially reflected at the 

 interface MGN and form a divergent bundle of light which passes 

 through the aperture CD. Thus the light which comes from a point in 



E B 



Fig. III. 13. Formation of the image of the opening in the condenser diaphragm 

 on the conjugate area in Frangon's hemisphere. A. The undeviated rays which enter 

 the hemisphere are parallel. B. The undeviated rays which enter the hemisphere 



converge directly on HI. 



the opening in the condenser diaphragm and which is not deviated by 

 the object specimen spreads over the field at CD and interferes with the 

 deviated light to form an image of the object specimen. 



The substage condenser and the diaphragm can also l^e so arranged 

 that an image of the opening in the condenser diaphragm is formed 

 directly on the conjugate area of the diffraction plate as is shown in B. 

 The rays then diverge from the conjugate area until they strike the 

 silvered portion of the hemispherical surface and are reflected as a 

 bundle of parallel rays. After partial reflection at the interface MGN, 

 the parallel rays emerge from the aperture CD. The undeviated light 

 spreads over the image plane at CD and interferes with the deviated 

 rays to form an image of the object specimen. This bundle of parallel, 



