SCIENCE IN THE INDUSTRIAL WORLD 



commercially. The credit for this belongs to Dr. 

 Robert Joly, of Dublin, although Mr. J. W. Mc- 

 Donough in America produced a practical screen- 

 plate about the same time. 



On Joly's plates "the three colors were arranged 

 regularly in lines, and were applied to the glass by 

 means of a ruling-pen Joly used two color- 

 screens a ' taking screen ' that was fixed in front of the 

 plate while the exposure was being made, and a 'view- 

 ing screen' which was put in front of the positive for 

 viewing the picture, and might be bound up with it 

 as a fixture, if preferred." 



By the use of ruling-machines, lines so fine that 

 forty could be put in a millimeter (more than a thou- 

 sand to the inch) were obtained, but even with these 

 it was not felt that the desired degree of tenuousness 

 had been reached. 



Several other methods of making line color-screens 

 have been devised, of which two, perhaps, are worthy 

 of attention. One is the recent invention of Robert 

 Krayne. "Sheets of celluloid are stained in the requi- 

 site colors and are then placed on the top of each other 

 and cemented together so as to form a continuous 

 block of red, green, and blue celluloid. A section is 

 then cut straight through this block, and a leaf ob- 

 tained which shows through its width the red, green, and 

 blue lines which were originally the leaves forming the 

 block. To make the Krayne mosaic screen these 

 lined screens are again cemented together to form a 

 block, and a section is now cut at right-angles to the 

 line direction." 



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