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The photographic news
- Bandzählung
- 29.1885
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- 1885
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1390, April 24, 1885
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The photographic news
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Band 29.1885
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- Register Index III
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THE PHOTOGRAPHIC NHWS, Vol. XXIX. No. 1390.—April24, 1885. CONTENTS. PAGE Captain Abney Lecturing at the Society of Arts 257 Platinotype Printing 258 Thumb-Nail Notes 259 Galton’s Composite Portraits. By W. E. Debenham 259 Remarks on Photographic Paintings, and Isochromatic Photo graphy. By W. M. Ashman 260 To the Capo. By C. Ray Woods 262 Carbon Printing. By W. Lang, Jun 263 Notes 26* Patent Intelligence 266 PAGE The Jewish Type, and Galton’s Composite Photographs. By Joseph Jacobs, B.A 268 Photo-Lithography and Phot-Zincography. By Major J. Waterhouse. B.S.C 269 An Attempt to Photograph the Corona. By W. II. Pickering 270 Mounting Large Photographs. By F. J. Haynes 270 Correspondence 270 Proceedings of Societies 271 Talk in the Studio 272 Answers to Correspondents 272 CAPTAIN ABNEY LECTURING AT THE SOCIETY I OF ABTS. It is only now and then that one sees the Lecture Room of the Society of Arts so full as it was on Monday last, when Captain Abney spoke of photography and the spec troscope. “ My text is the spectrum,” said the lecturer, “ and you see it on the focussing screen of this camera.” The source of light was an electric arc sustained by the battery of accumulators belonging to the Institution, and Captain Abney made the whole arrangement of apparatus (arc, collimator, slit, two prisms, objective, and camera) clear to his audience, so that the text was well impressed upon them, after which he exposed a plate to the spectral image, and very successfully developed it upon the lecture table. ‘‘Before telling you anything of the nature of the influ ence exerted by the spectrum upon the sensitive plate,” resumed the lecturer, “ let mo tell you something about matter itself.” Captain Abney then gave an exposition of the atomic doctrine, and pointed out that although this doctrine is based entirely on indirect evidence, it is one well worthy of consideration and study. He told his audience that they must try to forma mental picture of matter, and he would try and assist them in doing so. First, as regards mole cules. The molecules of which physicists suppose matter to be built up arc similar, insomuch that they all occupy the same amount of space, but their weights differ con siderably. A molecule may be —indeed, generally is—built up of several atoms ; but the atom is the ultimate and un- divisable constituent of matter. Sir William Thompson tells us something as to the probable size of molecules, but he does this with caution and reserve ; his figures are “ less in diameter than one two-hundred-and-fifty-thousandth of an inch, and greater in diameter than one twenty-five- thousandth of an inch,” and we may accept this estimate without more reserve than is usual in matters of scientific speculation. If we can imagine a globe of water the size of a foot-ball, magnified to the size of the earth, its molecular structure would become visible, aud we should find—according to Sir William Thompson's view—the molecules to be larger than small shot, and smaller than cricket balls. One more aid to the imagination. Let us suppose matter to be magnified to the utmost limit which is possible by the use of our best microscopes, and the magnified image to be again magnified to the same extent, then would the mole cular structure become visible. Every atom is charged with energy, but it is doubtful whether we ought to call this energy electricity, although, as in the case of electricity, we may recognise two equal and opposite forms of the molecular force. These we may call plus and minus, or positive and negative variations of the atomic energy, and when chemical combination occurs, the libei ated energy takes the forms of heat and light. “ See,” said the lecturer, “ I dust a little powdered anti mony into this jar filled with chlorine gas : now note how energetic the combination is, the bright white light showing the degree of heat generated by the combination, and the intensity of ths reaction. Next I will sprinkle some finely- divided silver into a similar jar of chlorine gas, and you will see that the reaction is not nearly so intense, only a dullish red heat being the result. In one case the penta chloride of antimony is formed by the combination of the antimony and the chlorine ; while in the other case, chloride of silver is formed by the combination of silver with the same halogen. The constituents of the former combination are held together with far more force than the constituents of the latter combination : the difficulty of separating the constituents of a compound being (with certain qualifi cations) proportionate to the energy manifested during their combination. Still, one must not suppose that attraction is the sole force which governs the molecular or atomic constitution of matter, as in reality there are also repulsive forces, and the contrary forces are oftentimes to be regarded as contending for the mastery. A striking experiment was shown to enable the audience to form some kind of a mental picture of this condition of things. In a glass cup placed on the stage of a vertical lantern, a number of small magnetic needles, each having a cork float at one end, were placed, and as the floating ends were all of similar polarity, they mutually repelled each other; but when a coil through which a strong electric current was passed was brought over the top of the glass, the floating poles were so strongly repelled to wards the middle of the field as to be held in this position, in spite of these mutual repulsions. By shifting the governing coil into positions where its action became less intense, the mutual repellant property of the similar poles became once more apparent, but was again overcome by including them in the intense magnetic field of the coil. It should be mentioned that Captain Abney used a de monstrating lantern of the form designed by Professor Morton, and we need do no more than give the diagrams on the next page to enable our readers to understand how —easy it is to use the apparatus either for horizontal objects as, for example, the magnets floating in a glass of water— or for vertical subjects. The audience were cautioned against taking a too realistic view of the possible movements of molecules or atoms, and to remember that in the case of the magnets used to illustrate the matter, the movement could only take place in one plane,
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