PRACTICAL PHOTOMICROGEAPHT. 



177 



Or an article variously known as a " parabolic reflector," a 

 "side reflector," or a "cup," may be used in conjunction with 

 a bull's eye. The action of the cup may easily be gathered 

 from our cut, Fig. 42. A. parallelizing glass will be useful 

 here also, and the radiant is to be placed on a line perpendicu- 

 lar to the optic axis of the microscope. 



Polarising apparatus in connection with photo-micrography is 

 often of great value, in the investigation of crystals and 

 crystalline matters. The worker in this line must be prepared 

 for considerable difficulties in color-rendering, but beautiful 

 and useful results have been achieved by some. It is important 

 to use prisms as large as possible, to consider carefully the 

 selenite to be used, and to study the best effects in color-rendering 

 that can be produced by modern photography. 



