154 



PROGRESS IN MICROSCOPY 



Fig. 4.34. Hilger and Watt interference microscope. 



Application of reflecting interference microscopes to micro-hardness tests 



Hardness of a material may be measured by the resistance it 

 displays against penetration of another material to which a given 

 amount of force is applied. In the Vickers method, the impressing 

 element is a diamond square-based pyramid whose vertex angle is 

 at 136^ Since the geometrical shape of the pyramidal impression is 

 known, its area is determined by measuring the diagonal of the square 

 base. Let F be the force exerted against the impressing element (ap- 

 plied by a weight) and 5 the impressed area, hardness H is educed by: 



H = 



(4.1) 



