SCIENCE IN THE INDUSTRIAL WORLD 



English scientist, J. Clerk-Maxwell, but in actual prac- 

 tice many difficulties were encountered in producing the 

 desired effects by such a process. A great number of 

 things interfered with the actual workings when it 

 came to apply pigments to the paper. For example, 

 the colors used must necessarily be absolutely pure 

 reds, blues, and yellows; and such colors, containing 

 no trace of any other color, were difficult to produce. 

 A great difficulty was also encountered in the mechanical 

 part of producing practical blocks for printing. So 

 that it was not until 1881 that practical color-printing 

 became possible. 



Experimenters both in Europe and America had been 

 working on the problem, but the first blocks that were 

 actually practical for this kind of work were perfected 

 by F. E. Ives, of Philadelphia, in 1881. This date, 

 therefore, with that of the discovery of the half-tone 

 process shortly before, marks an epoch in the history 

 of illustration an epoch of perhaps greater improve- 

 ments than any since the discovery of the possibilities 

 of reproducing pictures by woodcuts or metal plates. 



Knowing that every picture in color, no matter how 

 complicated its scheme, is simply a peculiar arrangement 

 of the three primary colors, it is obvious that if some kind 

 of substance which would allow the passage of the rays 

 of one of these colors and exclude those of the others, 

 could be found, then the position and amount of this 

 particular color might be determined. This of course is 

 not possible by the ordinary sense of sight any more 

 than it is possible for the unaided eye to determine the 

 composition of ordinary light. But by the use of prisms 



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