64 THE A B C OF PHOTO - MICROGRAPHY 



cannot be utilized with this objective of low 

 aperture; the flame appearing as a brilliant 

 line of light running across the field of view 

 from top to bottom with comparatively dark 

 spaces on either side. There are two reme- 

 dies for this trouble, one in racking the con- 

 denser backward or forward until an even 

 illumination of the field is obtained, the other 

 in removing the radiant to some fifteen" inches 

 from the microscope and interposing a bulPs- 

 ye condenser with convex surface turned from 

 the light in such manner as to render the rays 

 fairly parallel. Either plan is very good and 

 satisfactory. We choose the former on this 

 occasion and find the lighting of the field to 

 be all we could desire. The subsequent mani- 

 pulations are now about the same as those gone 

 through with in making our first negative. The 

 color- screen yellowish green as before is 

 placed in position, light and object centered 

 on ground-glass screen, sharp definition ob- 

 tained with gelatine screen and focusing glass, 

 plate holder attached loaded once more with a 

 Forbes orthrochromatic S, and we are ready 

 for the exposure. How long shall it be ? The 

 plate is of same sensitiveness as the other but 

 the light is more highly actinic than the Wels- 

 bach. On the other hand, the object is stained 



