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26 b!: 6 51 THE PHOTOGRAPHIC NEWS Vol. XXXV. No. 1687.—January 2, 1891. CONTENTS. Safe Development in Good Light 1 Photographic Reproduction of Literary Mattw"L"."3 Notes on Portraiture. By H. P. Robinson 4 Some of the Pendencies in Photographic Art. By Philip I. Newman 5 Miss Marr and her Detective Camera N 7 Notes g Impressionism in Photography."By George Davison 10 PAGE The Pictures at the Edinburgh Photographic Exhibition 12 The Awards at the Edinburgh Photographic Exhibition 12 Astronomical Telescopes. By A. A. Common, F.R.S., Treasurer to the Royal Astronomical Society 13 Patent Intelligence 13 Correspondence 14 Proceedings of Societies 15 Answers to Correspondents 16 SAFE DEVELOPMENT IN GOOD LIGHT. In the Photographic News Year-Book just issued, we gave full details in relation to the principles governing developing room illumination, and how to make a lamp which will give a practically uniform light from one year’s end to another, so that one element of uncertainty in developing is removed, and whatever may occur with the plates, the operator never has occasion to doubt the constancy of his light. Another and greater advantage of the plan is that, under a scientific system of developing room illumination, the photographer has the power of working in the maximum amount of coloured light which any par ticular brand of plates will bear, greatly to his com fort day by day, and to the benefit of his eyesight after the lapse of years. Another step towards the abolition of empiricism in developing operations is to make proper use of the uniformly steady and trustworthy coloured glow when it is employed. Acquaintance with a few leading principles in this matter will enable a photographer to develop his plates safely in the same light in which another photographer using the same plates might get pronounced fog. Fig. 1 helps to explain two principles, namely, the influence of the distance of the horizontal plate in the developing dish from the source of light, and the in fluence of keeping the plate as much as possible in a horizontal rather than a vertical position during deve loping operations. Let YF be a table six feet long, and A the source of light; with transparent coloured glass in the lantern, A is the flame itself; with a translucent coloured screen, it is a point on the sur- | face of that screen, such screens becoming themselves, for argumentative purposes, virtually the source of light. A photographic plate, BD, a foot square, is represented with its edge B at a distance of one foot from the point Y, which is directly below the luminous point A, and EF is another plate a foot square, with its edge E five feet from Y. The diagram shows that the latter plate has far less light acting upon it than has the first one ; the plate EF receives only the cone of rays represented by the angle AKH, whilst BD receives the cone of rays included by the angle AMN. Rapid plates, which would fog, say, if developed in the position BD, might, perhaps, be developed with absolute safety at EF, at the end of the table. With the same source of light, it might be unwise to develop slow landscape plates in the dim illumination at EF, when they might bear the brighter illumination of the position BD. By far the best way to develop plates of different rapidities with safety is to suitably vary the distance of the developing dish from the source of light, and not to alter the light itself. Whether the plate, in handling, be held much in a vertical or in a horizontal position, has an influence upon the amount of light it receives, consequently upon its tendency to get fogged. For instance, tilt the horizontal plate EF into the vertical position EW; the diagram, by the additional length RW, shows that it then receives about four times more light.