54 THE A B C OF PHOTO MICROGRAPHY 



the objective alone. This tube having been 

 thoughtfully blackened on the interior by the 

 makers, there is no necessity for lining it with 

 one of black paper or velvet. A useful hint 

 is thus conveyed to other makers, which it is 

 to be hoped they will not hesitate to improve. 

 If the microscope, camera and radiant are 

 set up so that the optical axis runs straight 

 through the center of each, as they should be 

 and as they are in this case, the circle of light 

 on the focusing screen will be the same, though 

 the image may not be in its center. This must 

 be effected by moving the specimen on stage 

 very gently and icarefully, since the 'slightest 

 motion is greatly magnified on the screen. 

 Here a well-made mechanical stage becomes 

 most convenient and important, but not hav- 

 ing one at present we must use our fingers as 

 delicately as possible. This is not difficult 

 with low powers, but requires considerable 

 practice and experience when the amplification 

 is high. The projected image is now in the 

 center of a well-lighted field, with the camera 

 extension sufficiently short to permit a ready 

 manipulation of the micrometer focusing screw 

 whilst examining it upon the screen. It will be 

 found difficult to distinguish details sharply or 

 clearly, owing to the ground-glass being too 



