INTERFERENCE MICROSCOPY IN TRANSMITTED LIGHT 



113 



Dyson has devised a Lebedeff-type interference microscope. To 

 secure substantial image duplication, thick plates are required: this 

 requirement is not consistent with powerful objectives. To obviate this 



Fig. 3.21. Smith interference microscope (C. Baker). 



stumbhng block, Dyson provides a half-sphere whose lower part 

 consists of the two interferometer plates. Owing to the half-sphere, 

 thick plates are between the specimen and the objective: the micro- 

 scope shows an interferential image. 



8. FRANCON'S COMPENSATED INTERFERENCE EYEPIECE 



The foregoing differential method is appHed to the interference 

 eyepiece whose basic birefringent element is Savart's polariscope con- 

 sisting of two identical quartz plates cut 45° from the axis and crossed 



