5? THE A B C OF PHOTO - MICROGRAPHY 



tive with a low power and without an eyepiece 

 by transmitted light, we may proceed to the 

 final and very important stages of exposure 

 and development. The holder, in which the 

 plate chosen for this negative (a Forbes or- 

 thochromatic S.) has already been put in the 

 dark-room, is attached to the camera in place 

 of the focusing screen, and an opaque card 

 inserted between the radiant and stage, to 

 cut off all light from the object. Now comes 

 the crucial question, which must be answered : 

 "How long shall the exposure be?" Al- 

 though the plate allows a very considerable 

 latitude in this important direction, it has its 

 limits. As a rule it is better to risk over- 

 rather than under-exposure, since the former 

 may be rectified to a considerable extent in 

 development, whilst the latter is remediless. 

 From previous acquaintance with the sensitive- 

 ness of this brand of plates and the brilliancy 

 of illumination on focusing screen, I am led to 

 the conclusion that the length of exposure, if 

 made without the color screen, should be three 

 seconds, and with it some ten seconds, as its 

 employment usually trebles the time required 

 when the screen is not used. Accordingly the 

 slide is gently withdrawn from the holder, and 

 after a moment's pause to allow subsidence of 



