INTERFERENCE MICROSCOPY IN TRANSMITTED LIGHT 



117 



brings under the condenser the lens affording the Kohler illumination. 

 The divergent lenses are used in dry-front objectives and the free 

 aperture in oil-immersion objectives employed under normal conditions. 

 The instrument then comprises the two independent units shown 



Fig. 3.26. Frangon"s compensated interference eyepiece (Barbier, Benard, Turenne). 



in Fig. 3.26: the interference eyepiece (unit O.,. S.>, O3. iPo), substituted 

 for the standard one and the compensator (unit 2*i, Sj), secured under 

 the condenser. Owing to the versatility of the compensating system 

 it may be fitted to almost all types of microscopes. 



9. L. P. JOHANSSON'S LNTERFEROMETER EYEPIECE 



This instrument makes use of the full image duplication process 

 with a Savart plate and a condenser illuminating-slit. A glass plate, 

 whose sides are not quite parallel, enables one to make measurements. 

 The eyepiece layout diagram is shown in Fig. 3.27. A prism Q (ordi- 



