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

the same journal has one other memoir, some additional facts relating to the habitudes of the hyposulphurous acid and its union with metallic oxides. This contribution is dated Slough, November, 1819. The true importance of these researches did not make itself manifest till some twenty years later, when the necessity of removing the unacted on silver salt from the developed image became apparent. Daguerre and Talbot’s methods, as first pro pounded by their respective authors, were far from perfect, being images not sufficiently fixed. Herschel himself called the attention of these investigators to his early experiments, and the employment of hyposulphite of soda for the final operations made the Frenchman’s and the Englishman’s processes thoroughly complete. As Herschel seems to have been the first to analyse coloured flames by means of a prism, it may be as well here to note the fact, although it may not strictly be termed photographic. In 1822, in the Edinburgh Royal Society Transactions, p. 455, a memoir is contributed on the “ Absorption of Light by Coloured Media, and on the Colours of the Prismatic Spectrum, with an account of a ready mode of determining the absolute dispersive power of any medium by direct experiment.” In 1827, Herschel, among other articles, wrote that on light in the “ Encyclopaedia Metropolitana.” Up to about this time Herschel had been an adherent of the emission theory of light; but the labours of Young and Fresnel had induced him to accept the undulatory theory. In 1832, a short communication in the form of a letter was made to the British Association at their second meet ing, which was held at Oxford. The title of paper indicates the subject matter, " On the Action of Light in determining the Precipitation of Muriate of Platinum by Lime Water.” Herschel went abroad in the latter end of 1833 to carry out a long-cherished desire to survey the heavens of the Southern Hemisphere. His destination was Feldhausen, six miles from Capetown, and here, for four years, were carried on those astronomical observations which will for all time be associated with the name of Herschel. I am not aware that during the period in question anything bearing sufficiently intimately on what may be called pho tographic research has to be recorded, although solar radiation observations were made from time to time. The third meeting of the British Association was held at Cam bridge in the month of June, 1833. Two papers were contributed by Herschel, “ On the Absorption by Light of Coloured Media, viewed in connection with the Undu latory Theory,” and 1 ‘ The Principle and Construction of the Actinometer.” It has to be noted that the instrument described was one destined to estimate the heating power of the sun’s rays, not what we photographers understand by the title. The former paper appears only in abstract in the Association reports, but was printed in extenso in the Lond. and Edin. Phil. Mag. and Journ., vol. iii., p. 401. Before the Royal Society, on March 14th, 1839, a paper was read by Herschel, entitled “Note on the Art of Photography; or the Application of Chemical Rays of Light to the purposes of Pictorial Representation.” At the outset the author states that his attention had been but recently called to the subject of Daguerre’s concealed photographic processes, and that he had not known that the question had been considered by Talbot, or by anyone in this country; as an enigma to be solved, a variety of processes at once presented themselves. First, the so-called di-oxidising power of the chemical rays in their action on recently precipitated silver chloride ; Secondly, the instant precipitation of a mixture of platinum chloride and lime water by light, forming an insoluble compound, which might be blackened by various reagents; and fourthly, the decomposition of an argentic compound, soluble in water exposed to light in an atmosphere of peroxide of chlorine. Confining his attention to silver chloride, the author inquires into the methods whereby the blackened traces can be preserved, and the unaltered salt removed. This state of things can best be brought about by the use of the liquid hyposulphites. The author then specifies other salts of silver more sensitive to light than the chloride, viz., the carbonate acetate and nitrate. Commenting on investigations to be made on the spectrum, he advocates that the spectrum be produced not by the prism, but according to Fraunhofer’s method, by the interference of the rays of light themselves in passing through gratings, and fixed by the heliostat. Accompanying the paper thus briefly referred to were twenty-three specimens of photographs, one a picture of the large telescope at Slough produced in the camera. Through the kindness of Prof. A. S. Herschel, I am enabled to show a photographic reproduction of the frame of the great telescope belonging, if not to this particular period of the year, at all events to several months later. The year 1839, I need scarcely remind a photographic gathering, gave to the world Daguerre’s method of securing “ sun pictures,” and as this had but recently been divulged before the annual meeting of the British Association, we find it engaging the attention of the Mathematics and Physics Section. Talbot’s remarks will be referred to when I come to deal with his work. Herschel’s contribu tion on that occasion was a letter addressed to the presi dent of the section, wherein he stated that in experiment ing with Talbot’s paper and exposing it to the spectrum he got coloured impressions. He also records the action of the red rays on paper which had, in the first instance, been exposed to light. On the 20th February, 1840, Herschel presented to the Royal Society a paper entitled “ On the Chemical Action of the Rays of the Solar Spectrum on the Preparations of Silver and other Substances both Metallic and Non-Metallic." The reading of the paper extended over three meetings, viz., 20th and 27th February and 5th March. The whole memoir is full of suggestive material; there is only time to note one or two of the more impor tant points. The terms positive and negative are here introduced for the first time to indicate respectively pic tures in which the lights and shades are the same as in nature, and in which they are the opposite (par. 8), and these distinctive terms remain with us to this day. The first part of the memoir is devoted to the fixing of photo graphs, and the comparative merits of hyposulphites, potassium iodide, potassium ferrocyanide, &c., are dis cussed. The bleaching of the image by mercuric chloride is here recorded (par. 19). The second part relates to the taking of photographic copies and transfers. The third treats of the preparation of photographic paper, the photo graphic possibilities of lead compounds. The author describes a method of precipitating on glass sensitive silver compounds, and refers to such films being likely to lead to an extension of the art of photography. After stating results of his experiments with iodide, bromide, and chloride of silver, he suggests that similar experiments be made with silver fluoride. Gold and silver salts were also experimented on. (To be continued.)