PHOTOGRAPHY 1()7 



of the microscope instead of the drawtube (and somewhat 

 similar miniature cameras are now offered by other makers). 

 The appropriate homal lens is first screwed in (there 

 being a low-power homal, one for the 10 and 20 apochro- 

 matics, and one for the high-power immersion objectives). 

 The microscope may be kept slanted; and the light, as for 

 observation, may come from a disc of illuminated double- 

 ground glass, diaphragmed to equal the field of view. 

 The focusing is accurately done (with distance spectacle 

 glasses) by observation of an already focused scale by a 

 lens through a side tube to which enough light is reflected 

 by a slightly silvered prism. A graduated wedge of tinted 

 glass is placed below the plate-holder, and a trial exposure 

 made, preferably much too long. When this test plate is 

 developed and fixed, an inspection gives the correct time of 

 exposure, and a second exposure is made without the wedge. 

 For an object with some depth, the focus can be suitably 

 altered during exposure, the manipulator watching the 

 alteration, meanwhile, by the side tube. Non-halation, 

 isochromatic plates are good; and rodinal is a useful 

 developer for these plates. The well-developed plates, 

 after drying, may have the surface of the film cleaned by 

 rubbing with a cotton cloth dipped in xylol. 



Negatives and Prints. — Mercury intensification may be 

 useful. These small plates may be made to give prints 

 three to five times the size, by the use of an enlarging 

 apparatus ; or, which is often better, enlarged lantern slides 

 may be made from them and negatives made from these. 

 Prints may be made with developing paper after the correct 

 time for each plate has been ascertained by trial. Over- 

 exposed or overdeveloped prints may be made use of, 

 after fixing, washing, and drying, by putting them in a 

 sufficiently dilute solution of iodine, and brushing them in 

 it, until they are just bleached enough, and then replacing 

 them in hyposulphite. They sometimes give the best 

 pictures. 



Stains and Screens. — In the writer's experience, prepara- 

 tions specially stained for photography, faint yellow or 



