160 THE PRODUCTION OF POSITIVES. 



Every part of the negative not required for re- 

 production should be masked, and all extraneous 

 light cut off. 



After focussing, the smallest stop compatible with 

 a proper differentiation of the several shades in the 

 negative should be inserted, and an exposure accord- 

 ing to the size of the enlargement and density of the 

 negative being given, the usual manipulations are 

 proceeded with. 



The advantage this method possesses over that to 

 be described, is the possibility of enlarging from a 

 negative of any size. This, however, can be accom- 

 plished by other means, and is only mentioned as an 

 additional resource where time is important, or 

 where the markings are so fine that they would be 

 injured by the coarseness of the film on dry plates, 

 when the collodion process is not available for the 

 production of a reduced negative. 



The easiest method when daylight is not available 

 is to place an ordinary magic lantern (the condensers 

 of which are not less than four and a half inches in 

 diameter) in the recess of the dark room. The 

 entrance of actinic light being prevented by fastening 

 the sleeve intended for the microscope over the noz- 

 zle of the lantern. 



The focus is obtained by pinning a sheet of white 

 paper on a moveable stand, and substituting the sen- 

 sitized surface for it after placing a cap over the 

 nozzle. The latter operation is much facilitated, if a 

 piece of ruby glass is let into the cap. 



