386 Transactions of the Canadian Institute. [Vol. VII. 



pure green patch on a white ground. The grounds in the three 

 negatives will be opaque : the patch in the red and blue-violet record 

 negatives transparent, and in the green record negative opaque. The 

 corresponding transparencies will have transparency of the grounds 

 from all three, transparency of the patch from the green and opacity of 

 the patch from the red and blue-violet record negatives. In positive 

 synthesis the ground will be composed of red, green, and blue light 

 superposed, giving white ; while the patch will be green since the 

 opacity of the other two prevents red or blue-violet from reaching the 

 retina or screen. In negative synthesis, in the superposed tran- 

 sparencies, the three grounds will be colourless giving white, while the 

 patch will be coloured blue-green in the transparency from the red, and 

 yellow in the transparency from the blue-violet record negative, there 

 being no colour from the green record negative. The superposition, by 

 negative colour mixture, of blue-green and yellow gives pure green. 

 The results are identical, visually, although they may be and, in fact, 

 are essentially different spectroscopically. 



An illustration of the three prints, in the complementary colours, 

 and of the finished picture resulting from their superposition is found in 

 the Plate. The method of formation of any colour in the picture by the 

 negative mixture of varying quantities of the three printing colours will 

 illustrate, better than any description, the reason for using com- 

 plementary colours in the printing or staining of the components. The 

 principal steps in making a transparency or print by the three-colour 

 process are illustrated in this Plate. The three negatives, without 

 colour of course, taken through the red, green, and blue-violet filters 

 illustrate the essential differences in densities due to different colours, 

 and indicate the general character of colour record negatives. The 

 separate prints are quite similar to ordinary prints from the above 

 negatives, but are in colours complementary to the reproduction colours. 

 The superposition of these three, or the printing of one over the other, 

 produces the finished picture. In the Plate the printing was effected by 

 three process blocks made from the three negatives, but it could be 

 accomplished photographically by using carbon tissues of the required 

 colour, and transferring them to a common support in accurate register. 

 Such a process would be exceedingly tedious and somewhat uncertain, 

 and an easier method is offered in three-colour transparencies or 

 lantern slides. Here three separate coloured films are made and 

 superposed giving, when bound together, the finished slide. The 

 examples of colour prints made by the writer are by this latter method 

 of superposing three transparencies, and can be projected upon the 



