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THE PHOTOGRAPHIC NEWS LNOvEMBER 16, 1883. asphaltum, which had been lying by for a few days, was taken, and rather less than half of it was brushed over with gum-water. When the gum was dry, some plain collodion was poured over, so that the plate was divided into three slips— a. Coated with collodion and gum. 6. Collodion alone. c. Asphaltum alone. There was also a little piece where there was only gum, but too small to notice. A piece of the thick reddish paper used for wrapping dry plates was now gummed down across the three slips, and when dry the plate was exposed to diffused light for about an hour, when a trial showed that the uncoated asphaltum was insoluble in turpentine. The gum and collodion were washed off with water, and the plate was dried and developed in turpentine. As the development proceeded, the asphaltum on the part a covered by the gum and collodion appeared decidedly more soluble than the uncoated asphaltum c, and, had time been allowed, would have developed quite clear. The un coated part (c) was just slightly soluble. The part (6) coated with collodion alone, remained the darkest, but this seemed to be due to the fact that the collodion had not been washed off, and had protected the underlying asphaltum against the solvent. In the part covered by the paper a very curious effect was noticed. The uncoated asphaltum dissolved readily, having been apparently protected from the light by the paper; but the asphaltum coated with collodion and gum remained almost as insoluble as the uncoated part fully exposed to light. In the slip (a), therefore, coated with gum and collodion, the parts exposed to light remained soluble, while that protected from it became insoluble, just the converse of the usual effect. The .general effect will be seen and understood from the diagram. The writer has not had time to further investigate and repeat the experiment, and therefore cannot offer any opinion as to the cause of the effect observed, but he hopes to do so at some future time. Brussels seems to be the most suitable city to choose for such a reunion ; the delegates will there meet with the most cordial hospitality, and a number of eminent men are on the spot to organise the undertaking. The ques tions to be solved are numerous, and it is difficult to find a practical solution of many. The units of measures, weight, light, and diaphragms, the question of legal copy right, dimensions of sensitive plates, &c.; all form a necessary part of the programme of subjects to be discussed. M. Scola's Monochromatic Lamp.—M. Scola, with the idea of furnishing a monochromatic lamp for laboratory use, has employed perchlorate of strontium dissolved in methylic alcohol for giving a red flame ; he has recently experimented in order to get a yellow flame for the same purpose, and has succeeded in so doing by replacing the above-mentioned salt by perchlorate of soda in the pro portion of 1} per cent, of methylic alcohol. It appears not to affect sensitive plates as Jong as they are not placed quite close to the light, and a yellow screen will effectually prevent any harm resulting. However, with the most sensitive plates, and the isochromatic plates, it is desirable not to be too hasty in adopting this lamp. M. Simonoff's Photometer and Shadow-meter.— M. Simo- noff has constructed an optical photometer based on a very ingenious idea. Its use is to calculate the relation existing between different degrees of light proceeding from the same source. It consists of a cylinder having at one end a translucid screen of opal glass, on which are traced several numbers, which can be clearly perceived by look ing through the tube like a telescope. It is directed towards the point the degree of light of which is to be ascertained, while behind the opal glass is made to pass a series of diaphragms of graduated sizes, multiples of one another. The diaphragms slide over until the figures can no longer be seen ; at the precise moment of this ob scurity the number of the diaphragm is noted. It is much the same in idea as Warnerke’s phosphorescent photometer. I have used it with success, and have made one more simple in construction than M. Simonoff’s. Of course it is liable to cause errors from a photographic point of view, as optical and actinic degrees of light are not the same. M. Simonoff has also constructed a little apparatus for determining the density of shadows, which he has called an ombrometer. A disc has from the centre to its circumference a series of gradated bands varying from light grey to almost black, each tint being separated from the other by a ring of white. In use it is placed horizontally, and in the centre a vertical rod is fixed, naturally casting a shadow which, on comparing its depth of tone shown on the white portions, will be found to coincide with one of the grey bands. Of course, by prac tice, one can dispense with these auxiliaries, but on cer tain occasions they are very useful. FRENCH CORRESPONDENCE. Photographic Society of FRANCE— Photographic Con gress at Brussels—Scola’s Monochromatic Lamp— Simonoff’s Optical Photometer and Shadow Meter— THIEBAUT's Pellicle Paper—Chapiro’s Photographs — MANDUIT and David’s Shutters. Opening Meeting of the Photographic Society of France.— This meeting, which took place on the 9th inst., is always hailed with joy as the time for new, improved, or perfected apparatus to be brought forward, and a lively interest shown in all applications of the art. The President announced the receipt of a letter from our friends of the Belgian Photographic Association on the subject of the proposed international photographic congress. This con gress will have the support of the Belgian Government, and this will give it a standing above any private under taking, and all other Governments are requested to send a certain number of delegates nominated by them. Thiebaut's Pellicle Paper.—This was the great attraction of the meeting. It is produced in sheets 45 by 55 centi meters. It has the advantage of being printable on either side, and to the touiist-photographer is invaluable. M. C. Chapiro's Photographs.—M. Chapiro, of St. Peters burg, has reproduced by photography compositions taken to illustrate a novel. The book is read to an actor, who puts himself into the desired attitude and expression, of which photographs are taken, and the work illustrated by the collaboration of writer, actor, and photographer. Shutters by MM. Manduit and David.—M. Manduit has made an improvement in the drop-shutter by adapting a little piston to the case of the lens, the other end retaining the elide. M. David has made a shutter giving definite exposures from I to of a second. It is a cylinder rotat ing on its axis, so arranged that each revolution is com pleted exactly in a second. Stopping points arc market on the cylinder corresponding to various durations, 2' •