THE ORCHID REVIEW. 3^3 



would only be a combined negative. Three positives must therefore be 

 made, and in these everything is necessarily reversed. We cannot now 

 reproduce the yellow patch just spoken of from the combination of red and 

 green without violet, but owing to the reversal we can get it by another 

 process, namely by printing directly in yellow, which is composed of red and 

 green without violet. Thus the yellow is also termed " minus-violet," and 

 correspondingly the pink is termed "minus-green," and blue "minus-red." 

 Now in printing the three positives in colour, first the minus-violet, second 

 the minus-green, and third the minus-red, the result in the case of the 

 yellow patch spoken of would be that the minus-violet, or yellow, alone 

 would leave an impression at this point, the pink and blue being passed 

 over blank, hence the original yellow would be reproduced. Whatever 

 amount of the primary colour sensations, separately or combined, was 

 present at any point of the original, these would be sorted out by the 

 selective influence of the colour screens, and re-combined in the subsequent 

 process to produce the original picture, even white and the darkest shades, 

 and thus an image of the original object is formed in its natural colours. All 

 these different details can be optically demonstrated in the triple lantern, 

 just in the same way that a ray of white light can be broken up into its 

 component elements by the spectroscope. 



The production of lantern slides or transparencies on the same principle 

 has already attained remarkable success. From the three negatives, 

 previously mentioned, three coloured prints are prepared upon special 

 transparent media, which when mounted in superposition exactly reproduce 

 the object photographed. These pictures may be viewed in the hand, or 

 used as lantern slides, and while as transparent as the best hand-coloured 

 slides are infinitely superior in delicacy of detail, some which we have seen 

 being remarkable for their life-like accuracy. The special form of camera 

 and the necessary materials can also be obtained, or the apparatus necessary 

 may be fitted to an ordinary camera. 



We believe that Colour photography is rapidly passing into the practical 

 stage, and we hope before long to see it applied more fully to the illustration 

 of our favourite Orchids. 



We may add that a most graphic lantern demonstration of the process 

 was given by Sir Henry Trueman Wood at the Royal Society's Conver- 

 sazione on May 14th last. The demonstration is thus described in the 

 Catalogue :— "The application of Photography to the production of Pictures 

 in Colour. — In the ' Three-colcur Process' three separate photographs are 

 taken by monochromatic lights corresponding to the three primary colour 

 sensations. These photographs in combination are then caused to 

 reproduce with approximate accuracy the natural colours of the object : — 

 (a) by illuminating three monochromatic positives with suitable coloured 



