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The photographic news
- Bandzählung
- 29.1885
- Erscheinungsdatum
- 1885
- Sprache
- Englisch
- Signatur
- F 135
- Vorlage
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- Hochschule für Grafik und Buchkunst Leipzig
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- SLUB Dresden
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- urn:nbn:de:bsz:14-db-id1780948042-188500006
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- http://digital.slub-dresden.de/id1780948042-18850000
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- oai:de:slub-dresden:db:id-1780948042-18850000
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- Seite I-II fehlen in der Vorlage. Paginierfehler: Seite 160 als Seite 144 gezählt.
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- Bandzählung
- No. 1406, August 14, 1885
- Digitalisat
- SLUB Dresden
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- Ausgabe
- Parlamentsperiode
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Zeitschrift
The photographic news
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Band
Band 29.1885
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- Register Index III
- Ausgabe Ausgabe 1
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Band
Band 29.1885
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- Titel
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522 THE PHOTOGRAPHIC NEWS. [August 14, 1885. cluster. When so fitted, the stand can be used as a walking stick or staff or alpenstock. The lower end of the staff is also provided with a removable cap or ferule. The wooden parts cau be slid outward so as to extend each section. The upper or inner end of each of the wooden parts is slit, and a spring is inserted so that the said part slides within the tube with an elastic friction. A cross wire or studs coming into contact with the ends of wires soldered in the tube or any other suitable stops, prevent the wooden part from being entirely withdrawn. I do not confine myself to the use of wood for the parts which slide within the tubes, nor to the round or cylindrical form of the folded stand, although I consider such form to be most suitable and convenient. The claims are— 1. The combination of parts constituting a camera tripod, or stand, formed, fitted, and arranged substantially as set forth and indicated hereinbefore. 2. In a camera tripod, the telescopic legs of the formation in dicated, substantially as and for the purpose set forth and in dicated. 3. In a camera stand, the formation of the telescopic legs so that when shut up and fitted together they form a walking stick or alpenstock, substantially as set forth and indicated. 4. In a camera stand, the camera top formed with spring jaws to engage with staples on the tops of the tripod legs sub stantially as set forth and indicated. NOTE ON PROFESSOR LEONHARD WEBER’S PHOTOMETER. BY BOVERrOX REDWOOD, F.C.S., F.I.C.* This instrument consists essentially of two tubes attached at right angles, in the form of the letter T, in such a manner that, while one is supported in a horizontal position, the other can be placed horizontally, or at any required angle. At the junction of the two tubes is a reflecting prism, by means of which, in combination with a diaphragm, the field of vision of an observer looking into an eye-piece, which forms one end of the movable tube, is divided vertically into two equal portions. One-half of the field is illuminated by the light passing through the movable tube, and the other half by light passing through the fixed tube. The source of the light passing through the fixed tube is a small lamp burning petroleum spirit. This lamp furnishes the standard light, and a scale is attached to enable the observer to measure accurately the height of the flame. Inside the fixed tube, between the petroleum lamp and the reflecting prism, is a frame, carrying in a vertical position a circular plate of opal glass, and travelling along the tube, from end to end, by means of a rack-and-pinion. At one end of the movable tube (the other end being furnished, as described, with an eye-piece) is a holder, in which a rectangular plate of opal glass (or, if desired, two or more of such plates) is placed. The petroleum spirit lamp having been lighted, and the flame adjusted to the height of two centimetres, the light to be measured is placed at a con venient distance from the rectanglar glass plate (usually 1 metre) and the eye of the observer being applied to the eye-piece, the travelling opal glass plate is moved by means of the milled head of the pinion until the two halves of the field of view are equally illuminated. The position of the travelling opal glass plate is then read off on the graduated scale attached to the fixed tube, and the illuminating power calculated by means of the table of values supplied with the apparatus. It is obvious that the travelling opal glass plate, being illuminated by the petroleum * A communication to the Society of Chemical Industry. lamp, becomes itself, to some extent, a source of light; and the amount of illumination of one-half of the field, therefore, depends partly upon the proximity of this plate. If it is found that the light to be measured is so powerful that the standard side of the field is not equally brightly lighted, even when the travelling plate is brought as closely as possible to the reflecting prism, at the junction of the two tubes, the light may, of course, be removed to a greater distance, or a second opal glass plate may be inserted in the holder. Under ordinary circumstances both tubes of the photometer are in the same horizontal plane ; but if it is desired to measure the illuminating power of angular rays, the movable tube, which is fitted with an arc divided into degrees, may be placed at any desired angle. The apparatus is also applicable to the measurement of diffused light. PHOTOGRAPHY AND THE SPECTROSCOPE.— LECTURE I.* BY CAPTAIN W. DE W. ABNEY, B.B., P.B.S. I will try to show you on the screen how we can picture the motion to ourselves. It is only a mental picture, but still it will give us a sort of idea of what happens. [An image was thrown on the screen by means of reflection.] In this circular glass trough of water is floating a little mag net, the magnet being held at the surface of the water by a cork. Passing round this coil, which is large enough to surround the trough, is an electric current from three Grove cells, and if I place it round the cell which contains the little magnet, and not quite on a level with the water, you will find that the single magnet goes into the centre of the water. It is repelled from the sides by the current that is floating round that wire. Well now, we have here one magnet. Suppose 1 put another magnet in. The ends attached to the cork have poles of the same name. They repel one another, to a certain extent, and yet the force outside makes them go as near one another as possible. By moving this coil vertically, we can make them separate and oscillate, and we can picture to ourselves the way in which two atoms in a molecule may oscillate, and be attracted, and yet repelled one from another. I put another little magnet in, so now there are three ; and here, perhaps, we have a picture of chloride of silver, which, I say, is composed of one atom of silver and two atoms of chlorine. We can still make them vibrate and oscillate. Here we have a mental picture—at least, it is a mental picture to me—of the way in which the atoms of chloride of silver may be made to oscillate. Again, I take four, and we repeat the same thing. Here we have a picture of ammonia— three atoms of hydrogen and one of nitrogen oscillating. And so I might go on. I might put five or six or a dozen in, and we. might get some idea of the way in which they would all oscillate. Here, then, we have endeavoured to draw from visible phenomena a mental picture of the way in which atoms of a molecule are vibrating. I must, however, call to your mind that those magnets are ' vibrating only in one plane, whereas, of course, the atoms of a molecule are vibrating, not in one plane, but in space of three dimensions ; but anyhow, I hope that you have got into your mind, at all events, the same kind of mental picture regarding the oscillations or vibrations of the atoms which I have in mine. I think that the case of the magnets is a particularly happy one, because, from all the evidence which we have at present, we are led to the conclusion that all atoms of matter are really charged with electricity, or what answers to electricity, of either one name or the other—that is, either positive or negative. Now, we will throw a spectrum on the screen. I will call to your recollection what it is. I am now going to send the light of the lamp through this bisulphide of carbon prism, and I need scarcely say that the prism has to play an important part in spectrum photography. The wave length of the red is about one forty thousandth of an inch, and the wave length of the violet, which is on the left of the screen, is about one fifty seven-thousandth of an inch. Each ray of light is transmitted in air at the rate of about 190,000 miles in a second. Thus the number of vibrations of the red rays is 500 million millions, and 700 million millions in the case of the violet rays, and this rapid succession of blows batters against anything upon which they fall. The mean violet, I may say, is the photographic light par excellence, and we shall recollect that such rays might beat upon the sensitive salt which we expose to it 700 million • Continued from page 509.
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