OCR Text |
Show 930 ON TRICHROMATIC PHOTOGRAPHY. [Nov. 28, represented as lantern-transparencies prepared from photographs of artistically preserved specimens, and also from the replica of a water-colour drawing of a group of these birds executed by Mr. J. G. Keulemans from living examples. Mr. Saville-Kent explained that all these photographs had been taken by him with the Sanger-Shepherd colour-screens, of which he exhibited a set, in conjunction with the Cadett " Lightning Spectrum-plate." These screens represented the three primary spectrum colours, red, green, and blue-violet, as enunciated by the late Prof. Clerk-Maxwell, and a separate negative of the subject had to be taken through each respective screen. The transparent positives prepared from these negatives were stained with tints complementary to those through which they were severally taken. That was-the positive resulting from the red-screen negative was stained blue or minus red; that from the green screen, red or minus green ; and that produced from the blue-violet screen, yellow or minus blue. Due care being exercised in obtaining the right tint-gradation, and the three stained positives being then superimposed in precise register, an optically perfect presentment or counterfeit of the original subject was mechanically produced. Tbe special method of developing and staining the positives exhibited was, as in the case of the production of suitable colour-screens, associated with the name of Mr. Sanger Shepherd, with whom Mr. Saville-Kent had been working in collaboration. It was recommended, for the acquirement of perfect registration, that all three of the respective negatives should be taken on a single plate in conjunction with a specially constructed multiple back, of which a sample was exhibited. This, however, was not absolutely necessary. It was competent, in fact, for anyone possessing an ordinary camera to secure correct colour-replicas of desirable objects, using only in conjunction with his instrument the Cadett spectrum-plates and colour-screens referred to. As an illustration of this fact, M r. Saville-Kent explained that the Peacock's feather, and several other subjects exhibited that evening, had been taken by him with a large-sized Kodak camera, across the lens of which he had simply slung, with the aid of elastic bands, consecutive sections of his multiple-back screen. The negatives taken for the production of these lantern-transparencies were also available for three-colour printing or process work. In conjunction more especially with such a perfected machine as the newly introduced Orloff Colour-printing Press, there was evidently a wide field thrown open for the cheaper reproduction, by printing methods, of Zoological aud Botanical subjects in their correct natural colours. For lantern demonstration, at any rate, the Sanger-Shepherd process as illustrated by him that evening would, Mr. Saville-Kent anticipated, strongly recommend itself to adoption by the many naturalists who had hitherto employed their cameras for the delineation in monochrome only of the subjects of their studies. In the instances, more especially, of the brilliant but fleeting tints of reptiles, fishes, |