52 ELEMENTARY PHOTO-MICROGRAPHY. 



photograph of some kind. Portraiture by day- 

 light, however, in a well equipped studio, gives 

 the operator a chance to model his sitter as he 

 pleases, and in this respect the conditions follow 

 more closely those under which a photo-micro- 

 grapher works when using artificial illumination. 



Photography through the microscope, of course, 

 can be done by daylight by means of a heliostat ; 

 and, indeed, some of the best known American 

 workers achieved most successful results when 

 using this instrument ; but it is only suitable tor 

 a specialist, and not to be recommended for 

 ordinary use. Apart, then, from sunlight, there 

 are many other sources of illumination, most of 

 which are efficient for all purposes. 



Artificial light has the decided advantage of 

 being more constant than daylight, from which 

 it follows that exact exposures may be repeated 

 successfully as often as required. Probably for 

 mere visual inspection of an object, almost any 

 kind of light will do, though even for this purpose 

 the best effect cannot be got unless certain con- 

 ditions are fulfilled. Defects not so readily observ- 

 able by the naked eye are accentuated and made 

 clearly visible on a photographic plate, so that 

 the art of illuminating an object properly is one 

 that must be learned before one can hope to 

 secure good negatives. The risk of failure may 

 certainly be reduced to a minimum, if only thorough 



