REFLECTED-LIGHT MICROSCOPY 



147 



the objective Oj) and the object P. Only low-aperture objectives are 

 suitable in this appHcation. 



Dyson's interference microscope (Fig. 4.28.) 



Three glass blocks cemented together. By. B^ and ^3, are inserted 

 between the objective Oj and the object P. The block ^3 is a 15 mm 

 radius-of-curvature plano-convex lens. The flat face MM' is semi- 



FiG: 4.28. Dyson interference microscope. 



reflective. The convex side of B^ is silvered, except in the polar area. 

 The block B^ is a parallel-sided plate on the top of which the small 

 area R is made highly reflective by an opaque metal layer. The utmost 

 thickness of B^ is slightly less than the radius of curvature of the 

 convex surface. The thickness of B^ is such that the curvature centre 

 of the convex side is about 1 mm above R. The rays originated from 

 P are reflected back by the convex side of B^ on to P' where P is 

 imaged by the system B^, Bo, B3. Then P' is observed through the 

 objective O^ of an ordinary microscope. The incident light illumi- 

 nating P travels in a direction opposite to the foregoing. After 



