85 



by the transmission, would also be reflected to the highest 

 degree. 



By the way of examination mentioned above, the different 

 colours are still only seen as rather faint tints of the pre- 

 dominant black colour; if we wish to see them especially marked 

 off alongside of each other, we shall have to use convergent 

 light and Nicol prisms, placed crosswise; the polarizer must 

 then be placed in a horizontal position in a stand before the 

 prism of the objective. The convergent light is produced by 

 using a strong objective. We shall then, when the light is 

 reflected from a bright plane, generally see a picture as the 

 annexed figure, that is, a semicircle with a bisected black 

 cross. 



P 



A — 



Fig. 32. 



PP and АЛ indicate respectively the directions of oscilla- 

 tion of the polarizer and the analyzer. The rays reflected near 

 these lines, will after the reflection keep the direction of oscil- 

 lation PP, and so they are completely absorbed by the analyzer. 



