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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
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- SLUB Dresden
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- urn:nbn:de:bsz:14-db-id1780948042-189100009
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- http://digital.slub-dresden.de/id1780948042-18910000
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- oai:de:slub-dresden:db:id-1780948042-18910000
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- Bandzählung
- No. 1703, April 24, 1891
- Digitalisat
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The photographic news
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316 THE PHOTOGRAPHIC NEWS. [April 24, 1891. designing such a lamp for lantern use has to contend. The essential feature of the arc lamp or regulator is the presence of two carbon rods, generally placed vertically one above the other. No light is apparent so long as these two carbons remain separate, and even if a piece of paper be the only screen between them, still no current can pass. But directly they touch, the circuit is completed, and if they are then separated the arc or arch of light plays between them. This arc is, however, almost non-luminous, the light being wholly derived from the ends of the carbon rods being brought to a white heat. If, however, from any cause the light should cease, the carbon rods must again be brought together to touch one another before the arc can be re-established. So that in every contrivance called a regulator or lamp, provision is made for the carbons to touch and then to separate from one another automatically, so that the arc can be maintained. If the carbons were to remain touching, they would simply turn red hot at the ends, fuse together, and very little light would come from them. If the reader will bear the necessities of the case in mind as just described, he will be able to appreciate the advantages of employing for projection purposes a lamp of the kind nowtobe described. It is in reality a combination of the arc and incandescent systems, and the quality of the light produced is superior to that given by either. This form of regulator, which is known as the electric sun lamp, was first introduced in Belgium about ten years ago. At once public attention was attracted to it—as it is attracted to anything new—and a few years later we find that the same lamp was awarded a gold medal at Paris. In 1882 it was first shown in this country, and everyone remarked how it differed from most other regulators in giving absolute steadiness of light. At the Health and Inventions Exhibitions at South Kensington it was again honoured by being medalled. But, although its construc tion showed much novelty and ingenuity, it had faults which prevented its coming into common use. These faults have since been remedied, and as we saw it in use a week ortwo ago at the St. Pancras Electrical Exhibition, we at once recognised its value for projecting purposes. The improvements have been carried out by Mr. F. R. Board man, and, without describing them in detail, we may say that the principal one is a provision for making the lamp automatic in its action—a quality which, before Mr. Board man took it in hand, it did not possess. As just explained, this lamp is a cross between the arc and incandescent systems, but possesses advantages which neither one nor the other alone can boast. The lamp consists of a small metal insulated box—that is to say, it is made in two parts, which are insulated from one another, but bolted together. Two tubes are attached to this box, one on each side, each tube holding a carbon pencil about four inches long and 8 of an inch in diameter. But the peculiarity of these carbons is, that one is hollow —that is to say, it is bored throughout its length, and an auxiliary carbon rod of less than a quarter of an inch in diameter slides freely in the tube thus provided. Another peculiarity which makes this form of lamp differ from all other regulators is the presence of a block of refractory material, which may be either a soft kind of Carrara marble, or an artificial stone resembling fire clay. Referring to the accompanying illustration, the lower carbon is solid, while the upper one has a hole through its length, as shown, and in this hole the sliding carbon rod is seen in section. There is an opening at one side of the marble block, and in the diagram it is shown how the rays of light proceed from that point. The action of the lamp is as follows :—The two carbon rods are kept at a fixed distance from one another by the marble block, which, it is seen, is excavated at top and bottom for their reception. It is, therefore, evident, from what has already gone before, that no light can come from them while they are separated ; but a sliding rod within the upper carbon furnishes the necessary initiatory touch. By the action of an electro-magnet, it automati cally slides through the upper carbon and touches its opposite neighbour. Directly this is done, and the arc established, it is drawn back by the same agency. When the arc is established, it plays within the opening in the marble block, and, therefore, brings that block to a white heat. The advantages of this form of lamp will be readily acknowledged by anyone who understands lantern work. To begin with, the light spot is small, and, unlike that afforded by many other electric regulators, it remains steady and in one position. The next point is that the somewhat cold glare com mon to arc lamps generally is modified by the presence of the refractory material, and the blue tone is changed to a some what warm light, more like that which is identified with the lime light. Indeed, in one respect, we may compare this lamp to a lime jet, although, of course, it is far more brilliant; for the Carrara marble, under the influ ence of the intense heat to which it is subjected, must be actually turned into the same material which is rendered incandescent in the older fash ioned light—viz., lime. And this forms rather a weak point in the newly devised lamp, because, when the marble is changed in that way and left idle, it becomes easily attacked by damp, and is apt to fall to pieces in a moist atmosphere. For this reason it is found essential, in some situations, to exchange the marble for a block of fire-clay, which is not subject in any way to atmospheric changes. To sum up the advantages claimed for this form of regulator for projection purposes, we may note first its great illuminating power, the colour of the light, and its steadiness. The great simplicity of the apparatus is the next feature to be considered, for really there is no mechanism at all if we except the electro-magnet for con necting the smaller carbon and the two simple springs which keep the two larger carbons firmly pressed into the cavities provided for them. The economy of the lamp, in comparison with other forms of regulators, is great; for it is stated that two four-inch carbons will feed it con tinuously for more than fifty hours. And there is no waste in these carbons ; they consume at the rate of one sixteenth of an inch per hour, and leave no residue. As the carbon is sold at one shilling per foot, it will be seen that the expense of this material for each lamp is under
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