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The photographic news
- Bandzählung
- 35.1891
- Erscheinungsdatum
- 1891
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- Englisch
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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. 1718, August 7, 1891
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The photographic news
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August 7, 1891. J THE PHOTOGRAPHC NEWS. 559 experiment, so far from upsetting our proof, tended to confirm it. When the penny was above the line of vision, it looked larger in proportion to the halfpenny than when it was below. Mr. Debenham said it should, and for once he is right, and it did, and does, as anyone can prove to his own satisfaction. Mr. Debenham’s great gallows machine is quite vitiated by the very simple fact that the structure compels one to look at the coins through an eye hole, the effect of which is to cut off that portion of the field of vision which causes the phenomenon observed. And this is “exact ” and not “loose,” nor “indefinite,” and this in science according to the gospel of the photographer. Mr. Debenham will find the answer to the rest of his paper in the replies to other critics. Finally, we beg earnestly—since life is short—that un trained and rash persons will not make it necessary for us to waste time in educating them. P.S.—We are glad to find such an authority on the eye as Dr. Griffith accepting our experiments and observations, but Dr. Griffith goes wrong in his deductions ; for, as he says, he is not an artist, or he would have known that the artist gives a compromise, and that the camera does not give correctly the proportion between near and distant objects, nor a compromise in any form. CITY AND GUILDS OF LONDON INSTITUTE. The following concerning the subject of photography is taken from the Programme of Technological Examinations. Among alterations and additions to which attention is called in a circular accompanying the Programme is the following:—“Practical tests have been added to both grades of the examination in photography, the syllabus of which has been rewritten.” I. SyUdbm.—Candidates will be required to pass both in the written and in the practical parts of the examination. The practical tests will be held on Saturday, May 7th, from 3 to 7.30 p.m. Ordinary Grade. (i) Written Examination.—The Written Examination will include questions founded on such subjects as the following :— (1) The studio and lighting of the sitter ; (2) the lighting of the dark room ; (3) the use of stops, shades, and “ instantaneous shutters,” as applied to lenses, and the use of the swing-back in the camera ; (4) a general knowledge of the practice and theory of the wet plate process ; (5) the practice and theory of the gelatine dry plate process—the composition of and defects in gelatine dry plates ; (6} various methods of fixing and intensifying negatives, with a general knowledge of the chemicals employed ; (7) silver printing, including vignetting and print ing in clouds, toning, and fixing ; (8) principles of retouching, spotting, and mounting prints. (ii) Practical Test.—Candidates may be required to show proficiency in conducting any of the following practical opera tions :—(1) To take in a studio -plate gelatine negative of some object to be indicated ; (2) to print, tone, fix, and mount a print; (3) to retouch and spot a negative ; (4) to test a sample of glass or fabric to be used in lighting the dark room ; (5) to make a lantern slide by contact. Honours Grade. (i) Written Examination.—In the Honours Examination, more difficult questions will be set in some of the subjects for the ordinary grade, and, in addition, a knowledge will be required of—(1) the theory of the photographic image, of development, and intensification ; (2) the theory' of light as applied to photography, including a general knowledge of spec trum photography, and the construction of lenses ; (3) the theory and practical use of sensitometers for testing speed and gradation of plates ; (4) the principles of photographic optics ; (5) the general principles of the Daguerreotype, and other nega ¬ tive processes which have been employed at different times ; (6) platinotype and carbon printing, preparation of a photo lithographic transfer, collotype printing ; Woodburytype and enamels ; (7) enlarging and making lantern slides in the camera ; (8) applications of photography to scientific purposes. (ii) Practical Test.—Candidates may be required to show proficiency in conducting any of the practical operations for the ordinary grade, and, in addition, the following :—(1) to take a portrait with some special lighting indicated ; (2) to find the focus of a lens either corrected or uncorrected ; (3) to test the sensitiveness and gradation of a plate ; (4) to copy an engrav ing suitable for the preparation of a lithographic transfer ; (5) to make a photo-lithographic transfer from a given negative ; (6) to make an enlargement from a 4- plate ; (7) to make in the camera a lantern slide from a negative. II. Full Technological Certificate.—A provisional certificate will be granted on the results of the above examination. For the full technological certificate in the ordinary grade, the candidate who is not otherwise qualified (see rule 37) will also be required to have passed the Science and Art Department’s Examination in the elementary stage at least, and for the full certificate in the honours grade, in the advanced stage at least, in two of the following science subjects :—1, Practical, plane, and solid geometry ; 8, light and heat ; 10, inorganic chemistry ; 11, organic chemistry. III. Worhs of Reference.—For the Ordinary Grade, “ Chem istry of Photography,” Meldola ; “Instruction in Photography,” Abney ; “Manual of Photography,” Hepworth ; “ Practice of Photography,” Chapman Jones ; “Silver Printing,” Robinson and Abney (Piper & Carter). For Honours, “ Researches on Light,” Hunt ; “Treatise on Photography” (Longman’s Text books of Science) ; Monckhoven's “ Photographic Optics ” ; “The Chemical Effect of the Spectrum,” Dr. Eder ; “ Light,” by Lewis Wright; Roscoe and Schorlemmer's “Inorganic Chemistry.” Absorption Spectrum and Colour of Liquid Oxygen —By K. Olszewski (Ann. Phys. Chern. [2], 42, 663—665).— In his former examination of the absorption spectrum of liquid oxygen (Abstr., 1887, 625), the author found bands corresponding with the wave-lengths 628, 577, 535, and 480. Liveingand Dewar (Abstr., 1891, 1), on examining the absorp tion spectrum of gaseous oxygen under high pressure, found the same four absorption bands in the visible part of the spectrum, and also two bands in the extreme red corresponding with the Fraunhofer lines A and B. The author has lately had occasion to prepare liquid oxygen in some quantity, and has repeated his examination of the absorption spectrum, more particularly in the extreme red. The column of liquid oxygen obtained had a thickness of 30 mm., and was 50 mm. in height. It was contained in a thin glass vessel surrounded by three glass beakers, in order to protect it, as far as possible, from outside heat. In this condition it was found possible to keep a sufficient quantity for the purpose, in view, under atmospheric pressure, and at its boiling point—181*4°—for over half-an-hour. The observations gave the four absorption bands before obtained, and also a fifth corresponding with the Fraunhofer line A. This band is of less intensity than those of wave-lengths 628, 577, and 480, but stronger than the band 535. An absorption band corresponding with the Fraun hofer line B was not observed. Liquid oxygen, as first obtained in small quantity in 1883, was described as being colourless. Since then the author has repeatedly had under examination liquid oxygen in larger quantities, and he has invariably noticed that a layer of greater thickness than 15 mm. has a distinctly blue colour by transmitted light. In the above experiments, in which liquid oxygen was employed in larger quantity than had hithert» been the case, the pale blue colour of the liquid was particularly noticeable. As special precau tions were taken in purifying the gas, and the absence of ozone was ascertained by special tests, there seems no reason to doubt that the colour observed is characteristic of oxygen in the liquid state. In the author’s opinion, the blue colour of the sky is, therefore, probably due to the oxygen in the atmo- sphere, since this element, at any rate in the liquid condition, is blue in colour.
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