58 ROYAL SOCIETY OF CANADA 
more accurate to give as good a result as the single aperture. There is 
little doubt that the most perfect prints will be obtained with single 
apertures. 
Fig. 24 is the square stop now used with cross-lined screens ruled 
diagonally. 
Fig. 25 is the same stop with four square apertures, requiring one- 
fourth the exposure of the first one. The number of apertures may be 

Fig. 24. Pre? 25: 
two, three, four, five or any other number; the rule is to dispose them 
like the squares of a chess board. 



FIG: ‘ RiGee 
