1 6 THE A B C OF PHOTO - MICROGRAPHY 



them corrected by any reliable optician. For- 

 tunately, no such procedures are necessary 

 with lenses of the present day. They are all 

 corrected with the view of being required for 

 photographic purposes, and their visual and 

 chemical foci will be found practically coin- 

 cident. 



The optical appliances thus far named are 

 absolutely essential for the prosecution of 

 photo-micrography by transmitted light with 

 transparent subjects, and by reflected light 

 with those of an opaque nature. These com- 

 prise the great majority with which the student 

 will have to deal, but there are many others 

 requiring particular illumination to bring out 

 certain details of structure which cannot be 

 done without special optical apparatus; as 

 the polarizer and paraboloid for dark field 

 effects. These will be more fully detailed in 

 the chapter devoted to illumination, but are 

 mentioned here in order to bring them to 

 notice under the head of optical appliances. 

 Both should form a part of the photo-micro- 

 graphic outfit of every serious worker. 



At the moment of writing this concluding 

 paragraph, I am informed by my friend, 

 Prof. M. L. Seymour, of Los Angeles, Cali- 

 fornia, that a very valuable optical accessory 



