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THE PHOTOGRAPHIC NEWS. Vol. XXIX. No. 1408.—August 28, 1885. CONTENTS. PAGE Roller Slide of Eastman and Walker 545 Lectures at the Finsbury Technical College 547 Collodio-Gelatine Dry Plates. By W. B. Bolton 547 On Developers. By W. K Burton 548 Red Prints for the Draftsman 550 Photography and the Spectroscope. By Captain Abney 551 Notes 552 Patent Intelligence 554 PAGE In Search of the Photographs at the Antwerp Exhibition 554 Orthographic Projection 550 Davenport’s Magic Lantern 557 Solubility of Paraffin Wax in Alcohol. By A. Haddon 657 Correspondence 558 Proceedings of Societies 558 Talk in the Studio 600 Answers to Correspondents 560 ROLLER SLIDE OF EASTMAN AND WALKER. Few photographic practitioners of the present day have very distinct recollections of the roller slide which was described in the Journal of the Photographic Society nearly thirty years ago (April, 1856), and before describing those mechanical details which make the slide of Eastman and Walker an instrument adapted to fulfil the every day requirements of the photographer, we give a reproductive sketch which accompanied Mr. Melhuish's paper of 1856. The paper, after sufficient for a fresh exposure has been wound off one roller and on to the other, is clamped against a sheet of glass by means of the screw, C. The Melhuish slide was, however, without any automatic apparatus for indicating when the proper length of the band had been wound off. This could not be determined by merely noting how much the rollers had been turned, as one roller is con tinually growing by receiving fresh paper, while the other is diminishing in diameter from the loss of paper. More recently, Mr. Warnerke constructed a roller slide, by means of which he took admirable pictures on a pellicle built up of alternate layers of collodion and india-rubber, and other flexible materials coated with sensitive com pounds ; and in this case the passage of enough tissue from roller to roller was indicated by the ringing of a miniature electric bell contained in the apparatus. The Eastman slide, which now comes from America, differs in essential features from those that have' gone before, not only as regards the design and working, but also from the circumstance that the parts are manufactured accurately to guage by machine tools, so that all parts of a given kind are interchangeable among themselves, a system of manufacture common in America. In arranging a roller slide to work on one of our usual field cameras (8 by 5), we did not avail ourselves of the suggestion of the Eastman Company, to fit the slide them selves, as to have the operation done by them was scarcely worth the delay of half a day or so which would have re sulted. The slide as sent out is furnished with a front piece which will generally require cutting down to fit it to a camera, and after about a few minutes had been spent in planing down the face until the surface of the paper corresponded with the position of the rough surface of the focussing glass, there was nothing more to do but to so cut off the excess wood from the edges, by a few runs on a small circular saw bench, that the instrument would slide into the runners of the camera. All this occupied perhaps ten minutes, but without the circular saw it might have taken half an hour. Before taking the apparatus out, we weighed it, and found that the roller slide, when charged with a roll of sensitive paper for 24 exposures (8 by 5), weighed 48} ounces, while two ordinary slides with two plates in each (4 exposures) weighed practically the same, or 48 ounces. At this rate, the slides and plates for 24 exposures would have weighed no less than 288 ounces. It is, however, in taking an extra stock of exposures that the value of the tissue becomes more strikingly apparent, as the case hold ing an extra roll for 24 additional exposures only weighs 54 ounces, as against about 7 lbs. for two dozen plates with their packing. The whole series of 24 exposures were made by the river side in the course of half an hour, and in the case of a procession or regatta, where one adjustment of the camera is sufficient, it would be easy to expose for 24 negatives in a couple of minutes or less. Being close at home, there was no inducement to pack the roll of sensi tive paper (or part of it) back in its case, and send it by post; a course which suggested itself as likely to be that which a newspaper correspondent would adopt were he using the apparatus. The development was effected with a sulphite of soda and soda developer, and a large number of sheets (cut off the roll with a pair of scissors) were developed in one deep dish, no harm resulting from the sheets overlapping, as long as the dish was kept in motion; in fact, the deye-
