The photographic news

• Bandzählung: 35.1891
• Erscheinungsdatum: 1891
• 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-id1780948042-189100009
• PURL: http://digital.slub-dresden.de/id1780948042-18910000
• OAI: oai:de:slub-dresden:db:id-1780948042-18910000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

212 THE PHOTOGRAPHIC NEWS. [MARCH 13, 1891. the Liverpool Astronomical Society, when a paper was read on “ Celestial Photography ”:—“ At a joint meeting of the Literary and Philosophical and Astronomical Societies of Liverpool, Mr. Herbert Sadler, F.R.A.S., read a paper on ‘ Celestial Photography,’ in which he referred to the great advances which had lately been made in astronomy by the assistance of photography. Starting from the first crude and imperfect pictures of the sun and moon, astronomy and photography had marched hand in hand until the present methods of manipulation enabled us to photograph objects which the eye can never hope to see. The paper was profusely illustrated by celestial photographs; and, in calling attention to a picture of Capella, Mr. Sadler explained that the rays which affected the plate started on their errand during the battle of Waterloo. As an illustration of the far-reaching power of the photographic eye, the map of the Pleiades constructed by M. Wolf contained 671 stars, and, after a careful sounding in this direction with the largest telescope in the Paris Observatory, the author felt assured that all beyond was darkness, and that he had absolutely reached the utmost depths of space; but a photograph of the same district taken by the Brothers Henry, with a much smaller telescope, in one hour showed 1421 stars against the 671 which had taken M. Wolf three years to map.” Not until Mr. Scott Archer, a London chemist, dis covered, in 1851, a practical method of utilising a solution of guncotton in ether and alcohol, known as collodion, for creating a surface on which sun pictures might be pro duced with greater rapidity and beauty than formerly, did photography begin to make giant strides, and during a period of thirteen years his principle of a nitrate of silver bath as a sensitiser remained in force. But the times were marching on to greater development, and it was by the hand of the 1888 president of the Liverpool Amateur Photographic Association, Mr. B. J. Sayce, that the first practical negative emulsion process, which he called collodio-bromide, rendered the manufacture of dry plates simple, trustworthy, and inexpensive. This process was introduced in September, 1864, and after several modifi cations by the author, the principle of emulsion versus the nitrate bath revolutionised photography, and enormously increased the army of amateurs. Various improvements in manipulation have been introduced, and bromide emulsion is the process of to-day, but the vehicle for the suspension of the silver salts is gelatine. Twenty-one years later the jury of the International Inventions Exhibition, held at South Kensington in 1885, granted to Mr. Sayce a gold medal and diploma for the discovery. Messrs. York and Son are keeping pace with the times by turning out lantern slides relating to the life of John Wesley at this, his centenary epoch. Photographs on Looking-Glass.—Mr. Marcus Guttenberg, of Manchester, has sent us for inspection some of his coloured photographs on mirrors, produced by a process described a few weeks ago in our patent reports. Those with sharp edges somewhat resemble the paintings on glass now so common, and in which the effects of reflection at the edges are prominent and do not agree with each other, like the natural tail of the organ-grinder’s monkey, and the tail of the red coat in which the little innocent is dressed. In another class of pictures by Mr. Guttenberg this objection is not prominent ; he, in this case, first deadens the front surface of the mirror with hydrofluoric acid, then applies an oval background, getting pictorial results somewhat better than we chance to have hitherto seen on mirrors. PHOTOGRAPHIC CHEMISTRY. I. Last Monday night Professor Meldola delivered the first of three lectures at the Society of Arts on “ Photographic Chemistry.” Mr. Francis Cobb presided. The lecturer stated that of late years the applications of photographic processes in art and in science have been numerous. Photography now claims to be a branch of science, and that it should be taught as such ; indeed, some progress has been made in this direction at certain schools and colleges in this country, but not nearly to the same ex tent as at the Technical High Schools of Berlin and Vienna. In this matter of education, it must be admitted, we have taken a secondary position, although this is the country of most of the great discoveries in photography since the days of Niepce and Daguerre ; silver printing on paper, the blue process, bichromated gelatine processes, pigment processes, emulsion processes, and Willis’s platinotype process originated here. Photography also has its physical side, and that should be taught in a scientific manner. In some minds the idea of technical training is connected exclusively with the teaching of handicrafts, but this is a mistake, and especially so in relation to the training of photographic technologists. One might begin the training by teaching the student the action of reducing agents upon silver salts. By adding ferrous sulphate to silver nitrate in a test tube, he would find silver to be precipitated as a grey deposit, finely crystallised. He might then be made to prove by tests that the deposit is really metallic silver. He might be instructed as to the action of reducers upon silver haloids, and that by submitting reduced silver on paper to action of solutions of gold or platinum, the dark deposit becomes more insoluble in nitric acid, proving that more or less of one of those metals has been substi tuted for the silver. He might be taught that the reducing agent becomes oxidised while doing its work, and how to prove this point in the case of an iron developer by the application of the ferrocyanide of potassium test. It is believed that silver can be thrown down in differ ent states of aggregation; ferrous sulphate throws it down from the nitrate in a grey crystalline state, but ferrous acetate throws it down from the nitrate in a fine and black condition. Such phenomena as these do not find ex pression in ordinary text-books ; the deposit is said to be metallic silver in both cases, but in the last one there may be some trace of organic matter with the silver. Faraday has shown different forms in which gold can be precipitated, but on the other hand, silver and its salts have a special tendency to bring down traces of foreign matter. Similar actions occur in dyeing. Mr. Roberts-Austen has shown how the most minute traces of an impurity in a metal will sometimes affect the physical characteristics of the whole mass. In the case of Carey Lea’s deposits from the organic salts of silver, the lecturer did not think that there was sufficient evidence that the precipitates consisted entirely of pure silver. Carey Lea had analysed some of the precipitates, and found in them 98’75 per cent, of silver, but Mr. Roberts-Austen had shown that two-tenths per cent, of lead in gold were sufficient to make gold brittle. A Dutch chemist, who has been repeating Carey Lea’s experiments, and analysing the deposits, says that the latter always contain traces of iron as an impurity. The student might be made to study the various actions