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The photographic news
- Bandzählung
- 24.1880
- Erscheinungsdatum
- 1880
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- Englisch
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- F 135
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1132, May 14, 1880
- Digitalisat
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- Paginierfehler: S. XII als S. XX gezählt.
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Zeitschrift
The photographic news
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Band 24.1880
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- Register Index 631
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Band
Band 24.1880
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238 THE PHOTOGRAPHIC NEWS. [May 14, 1880. the charge, I may be permitted to say one more word. If any thing were wanted to show that “ An Operator ” is not true to himself, it is afforded in his last letter. He wants to know how it is possible, under present circumstances, to perfect his knowledge in photography. “As for the chemistry of the process,” he says, “that is never thought of for a moment.” By whcm ? I should like to know. Evidently not by your correspondent ; and yet if he wanted to better himself in this respect, there is just now plenty of oppor tunity for learning photographic chemistry. I have seen several announcements of lectures in your columns only lately. I wonder how they will be supported.—Faithfully yours, An EMPLOYER. Hroreebings of Societies. Photographic Society of Great Britain. The monthly meeting of the Photographic Society was held on Tuesday, at 5a, Pall Mall East, the President, James Glaisher, Esq., in the chair. Mr. WARNRRKE read a paper on the “ Production of Photo graphs by means of a Phosphorescent Surface such as Balmain’s Paint.” Lieut. Darwin exhibited a negative produced by the same means. His process differed from that of Mr. Warnerke in the fact that while the latter aimed at the production of a transparency, the former produced a duplicate negative. Lieu tenant Darwin’s method consisted in exposing a luminous sur face to light, placing it in a printing-frame on the top of a nega tive with a sheet of red glass on the further side, and allowing the red light to pass through the negative for ninety seconds, thus blotting out all the transparent parts, the negative being made for a gelatine plate. Lieutenant Darwin remarked that he thought the want of sharpness spoken of by Mr. Warnerke was not due to the focussing, but to the roughness of the lumi nous surface. If the latter was the case, he feared much could not be done with the process. Mr. W. Bedford had made a few experiments in this direc tion, and had hoped to be able to make instantaneous exposures, but had found this was not possible. He believed the reason was, as stated by Mr. W arnerke, that the luminous surface was too coarse. Mr. Warnerke observed that in his opinion the want of sharpness was due to the fact that the focus of the luminous surface, when the camera was used, was different from that of ordinary light. He had produced transparencies by contact which were absolutely sharp, though he did not think the paint as prepared by Balmain was sufficiently fine for the purpose. The President having suggested an adjournment of the dis cussion of the subject until the next meeting, Captain Abney read a paper by the Rev. F. Hardwich, on the “ Oxyhydrogen Light.” The chief points of the paper were that while the preparation of oxygen was not unattended with danger, the manipulations of the oxy-hydrogen lamp might with safety be entrusted to beginners. Mr. Hardwich spoke highly of the new lens recently described by Mr. Dallmeyer. Captain Abney said he had received a letter from Mr. Hard wich in which that gentleman hoped that any member who had had experience on the subject would give his opinion as to the best angle to which the flame should be bent so as to give the best results. Mr. Cadett could not agree with Mr. Hardwich as to the im munity from danger in the exhibition of the oxy-hydrogen lamp. Some time ago he had experienced an explosion without any previous warning, so far as the light was concerned. He had been sitting on the bag previously, but he could not see how that could have caused the explosion. It had been suggested that when he got up from the bag there was a “ suck back ” ; but if this had been the case every one accustomed to oxy hydrogen work knew there would have been a slight " pop * at the flame, which was not the case. He believed that after a time the gases mingled, and he would suggest that the residue of the gas in the bags after exhibition should be analysed to settle this point. Mr. Newton said that with regard to the angle of the jet, it must not be too sharp, or a shadow of the flame would be thrown on the picture. The angle should be as short as it could conve ¬ niently be made. He quite concurred with Mr. Cadett as to the danger of inexperienced persons using the oxy-hydrogen light, and referred to several instances where serious accidents had occurred. He really thought Mr. Hardwich’s statement should not be allowed to go forth to the public without some modification. In the manufacture of oxygen he considered that the delivery pipe should be at least half an inch wide, and that granulated and not powdered oxide of manganese should be used. The latter was carried off by the steam generated, was deposited in the delivery tube, which it clogged, and hence an explosion ensued. With regard to pulverised chlorate of potash, it was quite true that it gave off oxygen rapidly, but it did not keep, and in his own practice he had found it more convenient to use it crystallized. As to the breaking of eondensers referred to by Mr. Hardwich, he did not think it was due so much to the heat as to the cooling. Lantern exhibitions were generally given in the winter, and when the light was turned out, the lantern door opened, and the audience had left the room, the cold frosty air caused the condenser to cool unequally, and so a fracture followed. As to storing of gas, he did not believe xygen could be kept in bags for more than two days, and if used after this time the common air which had got in would cause a disagreeable whistle. Mr. Bolas remarked, with regard to Mr. Cadett’s experience, that he believed the explosion was caused through inflammable dust in the bag. This dust was caused by the action of chlorine on the india-rubber, and he had known as much as half a pound to accumulate. No doubt when the pressure was removed from the bag a cloud of dust arose, and hence the explosion. Mr. H. Baden Pritchard said the suggestion of Mr. Cadett as to the analysis of the residue gas was a very important one, and he hoped it would be carried out. Mr. Dallmeyer hoped that for the future the name magic lantern, as applied to the oxyhydrogen light, would be abolished, and that it would be known as the optical lantern. Mr. Newton pointed out that the dust referred to by Mr. Bolas did not come so much from the india-rubber as from the canvas lining of the bag. In reply to Mr. Bolas, Mr. Spiller said it was quite true that chlorine and oxygen formed a combination with india-rubber. Captain Abney observed that a similar action was set up with ozone. He would like to ask Mr. Newton what had been his experience with condensed gases sent out in iron bottles. Mr. Newton said that in inexperienced hands it almost always failed, because, unless very great care was exercised in turning up the jet, the pressure was so great that it frequently ripped up the india-rubber tubing. Of course, did an explosion occur through the intermixture of these condensed gases, the consequences would be very serious. Mr. CADETT observed that, in spite of the danger, ha knew a gentleman who always used the condensed gases in a mixed state. After votes of thanks to Mr. Hardwich and Mr. Newton, an exhibition of instantaneous shutters took place. Lieut. Darwin showed a shutter which worked by electricity. The shutter was constructed by his brother, Mr. Horace Darwin, in connection with determining the altitude of the clouds, an investigation which the Meteorological Committee of the Royal Society had undertaken. The conditions to be fulfilled were that two cameras must be exposed by the same person, and exposed either simultaneously or at variable intervals, and this shutter fulfilled these conditions perfectly. Mr. Warnerke then gave the results of some experiments which he and Mr. Cadett had made with various instantaneous shutters. Mr. England’s shutter they found required but one twenty-fifth part of a second for the sky, and one-fifteenth for the foreground. Col. Stuart Wortley’s one eighty-fourth and one- sixty-seventh respectively. Mr. Harrison’s shutter they could not determine, in consequence of the shaking of the camera. Mr. Rouch’s double flap required one-fifteenth of a second, and Mr. Cadett’s one-fifth (the weather, however, was bad in this instance). He (Mr. Warnerke) thought that the great want in an instantaneous shatter was the power of graduating the exposure from the greatest rapidity to comparative slowness, and to bo able to record the length of lime in each instance. Mr. Cadett was engaged on such a shutter, and would exhibit it at the next meeting. Mr. England then showed his insta ntaneous shutter by means of a movable slit, in which he could vary the size and shape ot the opening. A noticeable feature in Mr. England’s camera was the sunshade attached in front, by means of which he could cut on the sun from the lens.
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