The photographic news

• Bandzählung: 6.1862
• Erscheinungsdatum: 1862
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: SLUB Dresden
• Rechtehinweis: Public Domain Mark 1.0
• URN: urn:nbn:de:bsz:14-db-id1780948042-186200003
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• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
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• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

September 19, 1862.] THE PHOTOGRAPHIC NEWS. 453 Gorrespondente. lessening or widening the interval between the pupils. This disposition or turn of the eyes is attended with a sensation, which seems to me, to be that which in this case brings the idea of greater, or lesser distance into the mind. Not that there is any natural or necessary connection between the sensation we perceive by the turn of the eyes, and greater or lesser distance. But because the mind has by constant experience, found the different sensations corresponding to the different dispositions of the eyes to be attended each by a different degree of distance in the object.”* These views of Dr. Berkley’s, Sir David Brewster, how ever, considers totally erroneous, and contends that our per ception of distance is not the result of experience. complete obscurity, and putting into a perfectly clean glass, a neutral. solution of nitrate of silver, then adding some drops of any organic or inorganic salt capable of deter mining a precipitate in the nitrate of silver : it is important for the nitrate of silver to be in slight excess to be assured that none of the precipitating salt remains in the super natant liquid ; 2nd. To expose this mixture to the sun for a few minutes, and shake it; 3. To take it back into the dark room, and then to pour into the glass either gallic or pyrogallic acid. It is well to solarize only one half of the mixture, but to add simultaneously to the two portions the same proportion of pyrogallic acid, to judge with cer tainty of the true alteration caused by light. M. Roussin made some experiments in this direction; the oxalate, tartrate, succinate, benzoate, carbonate, phosphate, and arsenite of silver, &c., are energetically reduced by a solari zation of a few seconds, and may be employed like the iodide of silver itself, with less rapidity, doubtless, for ob taining photographic pictures. This new path may lead to advantageous results. Perhaps, among the considerable number of insoluble precipitates of silver, substances will be found more specially impressionable by some rays of the spectrum, and capable thereby of being modified under the influence of certain hostile hues, green and yellow, for ex ample. Perhaps we may find among the very unstable com binations of silver a substance more sensitive than iodide of silver itself. Whatever it be, it is well ascertained that the employment of the iodides is not indispensable for obtaining images, and that the albuminate of silver well washed and dried, is decomposed like the iodide of the same base under the influence of light, and yields remarkable negatives. In a note presented to the Academy of Sciences, from M, H. Claudet, on the substitution of formic acid for acetic acid in the developing solution, the following advantages are claimed for the former :— 1st. The image appeal's as quickly as with the proto sulphate of iron and with greater intensity. 2nd. If the exposure has been well timed, there is no necessity for intensifying the negative, as is generally done when protosulphate of iron is employed. 3rd. The exposure is one-sixth of the time required for the ordinary process with neutral bath, and the developer of pyrogallic acid and acetic acid. We may readily conceive, that if a picture can be ob tained instantaneously under the glass roof of the operating room, and at a distance of twenty-five feet, a process of such great rapidity must be very useful for fixing the images of moving objects. THE GLASS ROOM—MODES OF LIGHTING. Sin,—I have been for some time past contemplating the erection of a glass room, and although, as an amateur, 1 shall require it chiefly for taking copies of various works of art, I should like it to possess the form and arrangement by which I may also secure well-lighted and pleasing portraits of my friends. On examining the various authorities for advice as to the best plan, I am a little bewildered by the general vagueness of the instructions given. In Mr. Lake Price’s book I find some useful hints, but he is not very precise as to the amount and position of the glass required. In your own pages, of which I have been a constant reader, I find a very valuable article on the details of construction, from which 1 intend to profit; but the article does not enter into the question of lighting in its artistic bearings. I have, however, gathered, from time to time, many useful hints on this part of the sub ject, scattered through different numbers of the News, Some time ago I read a very clear article on the subject, by Mr. Sutton, which appeared to me, at the time, most in accord ance with good sense of any which I had read; but from a subsequent remark in your pages, in answer to a correspon dent, I gleaned that you did not quite agree with the plan FOREIGN SCIENCE. [PROM OUR SPECIAL OORRESPOSDENT.] Paris, nth September, 1802. M. Roussrx has published some interesting observations Ipon the various salts of silver applicable to photography. He has lately given much attention to albumenized plates, and the best conditions for success in this branch of photo- graphy. In seeking to modify the proportion of iodide Usually introduced into the albumen, he remarked, that within certain limits the time of exposure varied in the inverse ratio to the quantity of iodide added. The greater the quantity of iodide, the less time is required for the light to impress a plate sensitized, washed, and dried. He also Temarked that, by considerably diminishing the proportion of iodide, and proportionally increasing the time of expo- Rure, he obtained images as vigorous, and blacks as intense 28 with stronger doses of iodide. This observation naturally led him to enquire if the presence of iodide of silver was Deally indispensable to the formation of the photographic Image, as hitherto supposed. It was very easy to solve this Auestion. He took the whites of new-laid eggs, and beat lhem into a froth without adding any foreign substance, tod next day covered several well cleaned plates with it. These plates, dried, immersed in a fresh bath of nitrate of tilyer, strength 8 per cent., and washed during four hours I several waters, then dried, were exposed in the camera tod developed in the ordinary manner, with gallic acid and litrate of silver. ’1The time of exposure was double or, triple that of an iodized albumen plate. The picture obtained Nas extremely vigorous, the blacks were unusually intense, tod a perfect harmony in the landscape was preserved. The Positive proofs obtained fronf these negatives were remark- Ably delicate, and entirely free from the pin-hole spots which 80 often invade the best albumen negatives. His singular fact, of a perfect picture obtained under the • Tinary conditions of photography without the aid of "ide of silver, naturally led M. Roussin to enquire if cer- SI salts of silver, did not, like the albuminate, possess the PToperty of being reduced by the action of gallic acid after Posure to light. Chemists must have long known that opdide of silver prepared in the dark and mixed with gallic t Pyrogallic acid and nitrate of silver keeps for a very long is without undergoing any alteration, while this same “de, exposed during a few seconds in the test-glass which dltains it, to the action of solar light, is energetically re- MMd by these same substances.t th his ready method of testing the photogenic property of neaasmnsoluble salts of silver is general, and permits our ni '? premising those which may advantageously be lineed with albumen before sensitizing to replace the alca- • “ '°dide. Every experiment consists—1st. In placing in Dubin, Frssay towards a New Theory of Vision, by George Berkley, M.A., tat"t gessential that the iodide of silver be perfectly washed, or, at least, Irefrav)n tains no. trace of alkaline iodide before solarization. It is also "IYer, 10 leave in the supernatant liquid a slight excess of nitrate of