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image of obliquely placed objects, the result being that only those rays which come to a focus nearest the flat plate are employed. At the same time, however, distortion is introduced, and the angle of view curtailed. Distortion.—When rays from an object fall obliquely on a lens, those which pass through the margin nearest that part of the plate where the image is formed fall on it, nearer the centre than they should do for correct propor tion, and those which pass through the opposite margin fall on it further off than they should do ; hence if a stop is placed some distance away from the lens, so as to use the margin to form portions of the picture, distortion is produced—barrel, if the stop is in front, and pincushion if it be behind. This defect is effectually cured by using two lenses with a stop between them. Inequality of Illumination.—This is produced by three causes:—1st, the more obliquely light falls on a given aperture, the less there will be transmitted; 2nd, the more obliquely a beam of light falls on a surface, the greater the surface it will cover ; 3rd, with inferior lenses the centre of the plate may be illuminated with reflected light from the lens (flare spot). Note.—It is particularly requested that all the members of the class will be present to-morrow, or the next Satur day, at 7-80. A METHOD OF TONING GELATINE TRANSPARENCIES. BY H. TRUEMAN WOOD. SUFFICIENT interest was taken in some lantern slides which I showed the other day at the Photographic Club to make it seem its worth to note the method by which they were pro duced, especially as there appears a general wish among the makers of lantern slides to substitute some warmer colour for the cold, often almost greenish black, generally found when gelatine is employed. The process used was simply the uranium process for the intensification of gelatine negatives, by uranium, described in Dr. Eder’s Modern Dry Plates. Having used it success fully for its proper purpose, it occurred to me to try whether it would serve equally well as a toning agent, and after a few trials it appeared that without much difficulty a series of warm browns and reds could be obtained, while in some cases a richer colour, even tending to purple, could be achieved. The plate is immersed in a solution containing 1 to 2 per cent, of uranium nitrate and a similar amount of potassium ferricyanide. The amount of the iron salt may vary considerably, and the colour of the resulting trans parency will also vary. The uranium should not be in excess, or the high lights of the transparency will be stained. If the slide be sufficiently vigorous in the first instance, toning with a weak solution gives a colour very like that of the admirable collodio-bromide slides of Mr. Brookes. If the slide be weak, and require intensification, the employ ment of a stronger solution gives a reddish brown, or rather a brownish red. The plate may be immersed in the uranium solution first, and the iron added ; and I am inclined to think this is the best plan. For most subjects these colours are evidently less appro priate than the ordinary black and white, but I think the variety that can be obtained by their use is pleasant in any case, and there are subjects for which the colour is a positive advantage. Dr. Eder speaks of the process as permanent; but of that I have no experience, never having tried the process at all till last autumn. HOW TO SENSITISE PAPER. BY HENRY J. NEWTON.* It may strike the reader of this heading as being quite absurd to be writing about how to sensitize paper at this late date, and * Photographic Timu. also as somewhat presumptuous in anyone to suppose that ther can anything be said, or any useful information given, upon a subject supposed to be so well understood generally by the pro fessional photographer. I will simply tell how I do it, and give my reasons why ; and if I succeed in convincing anyone that the reasons are good, and they are thereby induced to try my method, I think they will adopt it. For a long time the photo graphic mind has been almost wholly absorbed by the gelatine dry plate process, and now, after success has been attained in that direction, it seems to me a good time to explain how to use the negatives to the best advantage. A negative of itself is of little value or interest, neither is there any beauty in it, except to an experienced photographer. The business is carried on for the profit made in the prints from the negative ; therefore, he who can make the best prints will gain an enviable reputation and establish a business, other things being equal, when another, with equally good negative, would fail. The bath which I use is compounded as follows:— Nitrate of silver 40 grains Nitrate of ammonia 30 „ Liquid ammonia ... ... ... 2 minims Water 1 ounce This bath, you will perceive, is decidedly alkaline, and should be kept so by occasionally adding more ammonia, as the tendency is to become acid by liberating nitric acid by the decomposition of the nitrate of silver. I have become so used to the working of this bath, that I can tell by the appearance of the prints when it requires more ammonia. After you have compounded this bath, test its strength by the hydrometer, and make a note of the record in your memorandum book. The nitrate of ammonia is of less specific gravity than the silver, therefore it will not register so much ; but as in use the bath is not depleted of that salt, to strengthen, add more solu tion compounded as above, and then the silver nitrate until the hydrometer test indicates the original strength. This bath can be satisfactorily used until the silver is reduced to twenty-five grains to the ounce, and even less. The nitrate of ammonia, in conjunction with the silver nitrate, acts powerfully as a coagulator of the albumen, the consequence of which is that you get an uncommonly fine brilliant surface to your paper. Another and perhaps more important advantage of this bath is the fact that it does not change colour. An acid or neutral bath soon turns yellow or brown, and in a short time, especially in warm weather, becomes unfit for use, and has to undergo “ reconstruction,” by boiling or otherwise, whereas the bath I recommend can be used for a year or more, and remain clear and white as at first. Again, it is not necessary to fume paper sensitized on this bath, as it prints a deep, rich colour, and when used for printing from a weak negative, the print will be more satisfactory without fuming. For strong negatives I would, however, recommend fuming. To accomplish this, reduce the ammonia to one-half its riginal strength by diluting it with an equal part of water. With this diluted ammonia, fume in warm weather from fifteen to twenty minutes ; in cold weather not more than thirty or thirty-five minutes. I would advise any one using this bath to try it with and without fuming. The fumed paper tones in a little less time than the unfumed. To sensitize, let the paper lay on the bath about three minutes ; when taken off, jaise one end and press it against the edge of the dish until it adheres, then bring up by pressing against the paper until the end ofi t is above the edge; take hold of it then, and raise it gradually at a slight angle. The paper will adhere closely to the side of the dish by atmospheric pressure, and the surface will be free from any of the sensitizing solution. There will be no drip or waste. After it is hung up to dry, wipe the bottom edge with blotting or filtering paper, and it will dry in less than half the time that would be required if lifted from the bath in the usual way. This is quite important, not only saving time and sensitizing solution, but the fact that the paper dries quickly and is freed from any unnecessary excess of nitrate of silver is also impor tant, because it will remain white much longer, and conse quently be in better condition for printing should it become necessary to keep it two or three days after sensitizing. I have experimented with almost every printed formula for a sensitizing bath for albumen paper, but have found none which yields results so satisfactory as this one. The prints are peculiar for their clearness and brilliancy, and easy and satisfactory response to the effect of the toning bath.