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FEBRTARY 16, 1883.] THE PHOTOGRAPHIC NEWS. 105 I shall get some useful results,” he writes; and these he kindly promises to communicate when his research is com plete. Napoleon V. has been released by the French Govern ment. There was nothing to fear from him, since he never was popular, as any photographic publisher in France could have told the Paris authorities long ago. Portraits of Prince Jerome are a drug in the market, and we doubt whether it would pay any first-class photographer to invite the last champion of Bonapartism to give a sitting. Scolik, of Vienna, recommends the following method of recovering the silver from old plates and old emulsions. He collects all fixing baths, when these are no longer required, and puts into the liquid all waste films and spoilt emulsion ; the silver is, in this way, dissolved out, and only the gelatine remains. The silver iu solution is now reduced to a metallic state by putting into the liquid some fragments of zinc ; the precipitated silver is collected, washed in warm water to free it from any trace of gela tine, and then dried. The process has the obvious advantage that the silver is recovered in metallic form at a single operation. “ How stands the question of double dark slides versus changing-boxes?” we asked Mr. Meagher, the other day, no mean authority on the subject. Mr. Meagher was very decided in his reply : “I never make a changing-box if I can help it; but I have an order here for sixty double dark slides from one firm alone—Mr. Wilson, of Aberdeen—and, according to my order-book, double dark slides are the great want of the age just now.” Photography is to play a part at the approaching Electrical Exhibition in Vienna. In the first place, a gallery of paintings and photographs will be fitted up, in order to test the adaptability of various electric lamps to illuminate pictures; secondly, there will be photography practised by means of the electric light; and thirdly, there will, in all probability, be a photo-electric studio estab lishment for portraiture. A point of some interest to zoologists has just been set at rest by Captain David Gray, an experienced whaler, who has undertaken to prove that there is only one, and not two classes of the bottle-nose whale. Last season, it appears, Captain Gray killed upwards of two hundred of these creatures, and that indisputable proof might be at hand that these were really all of the same species, he caused photographs to be taken of every gradation of development showing the external characters and cranium of the animal at different ages. The pictures clearly demonstrate there is no actual line of demarcation, and that therefore there is only one species. Nature calls attention to the introduction of science among the subjects in which candidates for clerk-ships in the Civil Service may henceforth be examined. The step is no doubt a wise one, for a knowledge of natural science is, at any rate, as desirable as, say, an acquaintance with political economy, jurisprudence, and Grecian history. But our contemporary must not suppose there is anything novel iu the institution of a science examination for the Homo Civil Service. Such examinations were held by the Civil Service Commissioners more than twenty years ago. Professor McLeod, of Cooper’s Hill, has been studying the action of light upon india-rubber. M ■. Spiller has, on several occasions, pointed out the change that rubber undergoes in time, being transformed, not unfrequently, into a soft gummy mass, and for this reason photographers have been warned how they employ it as a preliminary coating for sensitive films. Prof. McLeod’s experiments were conducted, however, with rubber enclosed in glass tubes, some of which were hermetically sealed, and others plugged with cotton wool. Kept in the dark tor a couple of years, the rubber in these conditions underwent no change, but that “ exposed to air and light was covered with a thin brown coating, and, on being bent, this coating cracked ; the end which had been exposed to the light was rather brittle, and could not be stretched with out splitting.” Professor Boltzmann has succeeded in photographing the vibrations of sounds. To a thin iron plate, attached to a wall, and capable of vibrating to sound, he attaches a small thin platimum plate. The image of the platinum plate is first focussed on a screen by means of a solar microscope, and then a photographic plate quickly moved across iu the plane of the platinum screen by a strong spring, while the mouth-piece is spoken to. A boundary line between the lights and shadows is thus obtained, which forms a curve closely corresponding to the sonorous vibrations. As the photographic dealers now supply everything a photographer can possibly want, from a camel’s hair brush to a camera, it might be imagined that no one would take the trouble to make anything for himself when he can get it so much better and cheaper ready made. But this is not the case. In the pages of the English Mechanic are constantly to be seen anxious enquiries how to make all manner of things appertaining to photography, which almost suggests that the enquirers live beyond the ken of civilization, or have never heard of photographic dealers. Thus a gentleman who has been in the habit of making his own bevelled and gilt-edged mounts, complained recently that he never gets the edges quite straight, a result which may be readily believed when his method is to screw up about a dozen with thumb clamps, and work at them with a hand plane. Some one else coming to his assistance recommends him to buy a bookbinders’ cutting press and plough, which can be bought for about fifty shillings. This is good advice, certainly, but before laying out the sum, would it not be wise for the admirer of home made articles to first inquire how many bevelled and gilt edged mounts he can buy for the same money ?