263 



Photogrniih V is taken with the aid or convex lenses, focussing the 

 light from the snipliide screen on the plate; by means of a lead plate. 



one-half of the luminous screen was screened from the source in such 

 a manner as is shown in Fig. IV. A lilack strip of pajier is pasted across 

 the center of the screen to mark the halves of the luminous sulphide. 



