18 



AN ELEMENTARY THEORY OF PHASE MICROSCOPY 



through r', the undeviated rays diverge and spread with a high degree 

 of uniformity over the image plane. The rays belonging to the deviated 

 wave are drawn as broken lines in Fig. 1 1. 3. The deviated rays diverge 

 from the neighborhood of the particle. Subsequently they spread out 

 over the second focal plane of the objective. The deviated rays are 

 focused by the objective upon the neighborhood of the geometrical 



Condenser 

 diaphragm 



Fig. II. 3. Spatial distribution of the undeviated and deviated waves that arise 

 by diffraction at the object particle. Coherent light radiated from a point C in the 

 opening of the condenser diaphragm is incident as a substantially plane wave upon 

 the object particle and its surround. The stop S may assume different forms or may 

 be absent. The undeviated rays are drawn as continuous lines, and the undeviated 

 wave is distinguished by the expanding or contracting arcs. The undeviated rays 

 obey the laws of geometrical optics and so form an image C" of C in the second focal 

 plane of the objective. The deviated rays are drawn as broken lines, and the spatial 

 distribution of the deviated waves is indicated by the shaded area. The deviated 

 rays arise in the neighborhood of the particle and are converged by the objective 

 into the neighborhood of the geometrical image of the particle. 



image of the particle. A remarkable and important difference between 

 the undeviated and deviated waves consists in the fact that the undevi- 

 ated wave is concentrated in the second focal plane of the objective 

 upon the neighborhood of the geometrical image of the source of light and 

 is subseciuently spread out over the image plane, whereas the deviated 

 wave is spread out over the second focal plane of the objective and is 

 subsequently concentrated upon the neighborhood of the geometrical 

 image of the particle. 



Curiously enough, the quantitative relations between the amplitudes 

 and phases of the de^•iated and unde^'iated waves can be deduced from 

 the following simple considerations: Returning again to the wave that 



