146 



PROGRESS IN MICROSCOPY 



and Watt microscope is based on Michelson's principle. Baker's 

 microscope is based on either the Michelson or the Mirau principel. 



IVI 



Fig. 4.26. Krug and Lau interference microscope. 



Mirau's interference microscope (Fig. 4.27.) 



The principle of this instrument is the following: the incident 

 light-beam, emerging from the objective (9i, is split in two parts in 

 the semi-reflective plate G. One part is reflected on the object P and 

 the other in the area R of the front lens of the objective O^. This 



-7777777777777', 

 P 



Fig. 4.27. Mirau interference microscope. 



area, which extends over a small portion of the front surface, is made 

 fully reflective by an opaque metal layer. Both beams are super- 

 imposed anew as they enter the objective O^. The surface R is the 

 reference surface as was the mirror M in Figs. 4.23 and 4.24. The 

 horizontal plate G is inserted half-way between R (front surface of 



