Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/875

 PHOTOGRAPHY 839 Substance. Observer. Date. d th lene 18l&amp;gt;l 1837 1846 183(5 1813 1S04 1800 1722 1788 1789 1800 1812 1777 1806 1832 1814 1782 1782 1839 1782 1842 1 cent. A.D. 10th cent. 1684 1711 1782 1782 1836 18S3 iodine ai j Pelouze and Richardson . . Various other methyl compounds . . Cahours Torosewicz Hypochlorites (calcium and potass ium) Dobereiner Gehlen Molybdenate of potassium and tin salts Crystallization of salts under influ- ( ence of light j Phosphorus (in hydrogen, nitrogen, &c.) Petit Chaptal A. Vogel Scheele Ho (r s fat Vogel Fier Niepce Resins (mastic, sandarac, gamboge, ammoniacum, &c.) Hagemann Bitumens all decomposed, all resi dues of essential oils Da (r uerre Scnebier Similar colouring matters spread upon paper Pliny Eudoxia macrembolitissa (purple dye) Cole e &quot;y^&quot; ( Keaumur Nitric ether Senebier Henry & Boutron-Charlard Merk .. Bibliography. Hardwich and Taylor, Photographic Chemistry (9th ed., 1883) ; oney, Text-Book of Photography (1878), Instruction in Photography (1874 ; 6th ed., 1884), Emulsion Processes in Photos Billi Abr ed., 1884), Emulsion Processes in Photography (1878), and Photographic Optics, 1884 ; Burton, Modern Photography (3d ed., 1883) ; Robinson and Abney, Silver Printing (1880); Eder, Chemical Effects of the Spectrum (Eng. tr., by Abney, 1884); Hepworth, Photon: v.phy for Amateurs (1884); and Hunt, Researches on Light (1854). THE CAMERA. Any article descriptive of photography would be incomplete without a brief notice of the development of the camera. The inventor of the camera obscura was Giambattista della PORTA (q.v ), who was born at Naples about 1540. Except as a scientific toy, his apparatus was not of any practical use, though it is the parent of the apparatus which have grown up with photography. The principles which govern photographic lenses have been briefly given under LIGHT (vol. xiv. p. 593 sq.) and OPTICS (vol. xvii. p. 802 sq. ), and we need only state here that the finest camera which can be manufactured is useless unless the lens with which it has to be worked gives a flat field and an approximately If flio
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accompanying figure (fig 4), ac achromatic image. FIG. 4. Daguerre s Camera. M, stop of lens ; J, lens ; A, Dafuerre s camera ground glass plate, on which the image formed by the ^ ens ^ s thrown, and for which the sensitive plate is sub- stituted ; B, a mirror held at 45 by means of L, on which the operator viewed the image on the ground glass. The focus was obtained by sliding the inner box D towards cording to Hunt or from the lens (Photography, 4th ed., p. 39), by which it will be seen that at first the idea existed of moving the plate away from the camera. The first camera made in England, as far as is known, was that by Mr Palmer of Newgate Street, London, on the plan of Mr Fry and for him, in 1839. It was a very primitive apparatus, and was furnished with a lens made in the same year. The ordinary form of camera was simply a box, at one end of which was a lens, and at the other a ground glass for focusing, for which could be substituted a dark slide holding a sensitive plate. The adjustment of the focus was made by a rack and pinion motion attached to the lens. The arrangement, however, subsequently introduced for ob taining a rough approximation to focus was to have a sliding inner box as in Daguerre s camera ; and finally to obtain the greatest sharp ness the rack and pinion motion attached to the lens was used. It is evident that this form of camera has an advantage over the single box, since it allows more than one lens to be used. Ottewill s folding camera was a great improvement, in that, for outdoor work, it enabled a cumbersome article to be folded up into a compact space. Figs. 5 and 6 show it set up for use, and folded. A still more portable form was made by Mr George Edwards of Carlton Colville (Suffolk) in 1853, and for it he obtained the medal of the Society of Arts. Its portability is shown by the fact that for a 7-inch by 5J-inch plate its weight was only 2 ft 3 oz. Broadly speaking its principle was that of a couple of frames attached by screws to a solid bar, one of which carried the dark slide and the other the lens. The two were connected together and enclosed in a cloth bag, which in reality FIG. 5. Ottewill s Camera, set up for use. FIG. 6. Ottewill s Camera, folded. was the camera. This instrument is still used at the present day. It did not come into general use owing to its complicated arrangement of screws, for the main point in any camera is that there should be as few loose screws as possible. The next improvement is that known as the bellows form, originally introduced, it is believed, by Captain Fowke, R.E., about 1854. Its introduction maybe said to mark a new era in camera construction, and from that time to the present the bellows is to be found in nearly every improved form. After this invention the square instead of the tapering form of bellows was that most generally adopted. It is unnecessary to trace every improvement that has been introduced, but we give two typical FIG. 7. Hare s Camera. ones (figs. 7 and 8), which are manufactured by Hare and Meagher respectively. It will be noticed that in both these cameras there is an arrangement by which the focusing screens can be made to tilt at an angle with the axis of the lens. This is called a swing - back ar rangement, and is necessary when pho tographing architec tural subjects to pre vent vertical lines converging in the picture. When the ground glass is in a Fro. S. Meagher s Camera, vertical plane, no matter what tilt is given to the camera, vertical lines will always be shown as parallel in the picture. It will also be noticed that in these cameras there is an arrangement for focusing the lens by means of a rack and pinion motion in fig. 7, and by means of a screw in fig. 8. The gradual motion which can thus be given to the focusing screen is a great advantage, since lenses need not be constructed with rack and pinion mo tion. Many suggestions have been put forward for adapting FIG. 9. Marion & Co. s Camera. the camera for a developing chamber, and we believe Archer s could be used for this purpose. Mr Newton in 1852 introduced a camera in which wet plates after exposure were developed by dipping in troughs of solutions ; and we might name many others who sub-