122 



PROGRESS IN MICROSCOPY 



now be readily observed through the objective O^ of an ordinary 

 microscope. 



The plate Q^, identical with Q.,, is cemented against the condenser 

 which dispenses with diaphragming. 



-3 p 



Fig. 3.32. Fran^on interference microscope. 



Cementing a half- wave plate to Q^, the system QiQz becomes 

 a Jamin interferometer. 



Altering the former layout by rotating the plate Q^ 90° about its 

 axis, the on-infinity fringes developed are now perfectly parallel straight 

 lines. These fringes can be eliminated, and contrasts varied, by means 

 of a WoUaston prism set in the focal plane of the condenser C. 



12. MULTI-WAVE INTERFERENCE MICROSCOPES 



Let us consider (Fig. 3.33) the glass plates L^ and Z.., whose faces 

 opposite xx[ and x.^x'., are semi-reflecting and parallel. The mono- 

 chromatic light-ray S^^I^, incoming on the plate L., at /i, splits in two 

 rays: one transmitted, 7\, and one reflected. The latter reverts to the 

 first plate L^, is reflected, reverts on to Lo and splits again in two rays, 

 one transmitted, To, and one reflected. The same phenomena occur 

 for the other ray and, ultimately, a large number of transmitted rays: 

 r,, Ti, T3, etc. whose intensity naturally decreases as successive re- 

 flections occur. If incidence is close to normal, the rays T^, To, T;,, ... 

 can be much more closely packed than Fig. 3.33 shows. Provided 

 there is no phase object between the plates Li and L, and that a-i.v|, 



