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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1302, August 17, 1883
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The photographic news
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- Titelblatt Titelblatt I
- Register Index III
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524 THE PHOTOGRAPHIC NEWS. [AvaUsT 17, 1883. what disturb the just rendering of aerial perspective by the camera, the photographic picture often showing but little aerial depth when the eve almost loses the distance in a vague and cloud-like blue; while on the other hand, it sometimes happens that the photograph shows even near objects as surrounded in a veil or fog, although they may be clearly and sharply visible to the eye. The former conditions frequently obtain in mountainous districts where the air is pure, and its clear blue colour is scarcely affected by emanations from the earth; while the latter conditions are most strikingly illustrated when a slight yellowish mist pervails, or where the smoke from a town vitiates the atmosphere. It frequently happens, however, that the actinic transparency of tbe atmosphere is just such as to enable the photographer to perfectly render the aerial perspective with out exaggeration, either on the side of excessive shrpness as regards the distance, or of undue indistinctness of the distant objects. A FFINITY.—A term used rather vaguely in scientific literature, hut the following may be regarded as expressing the ordinary views. The various bodies which surround us are all formed of an in considerable number of simple substances or elements united one with the other in different proportions by certain forces, to which has been given the name of affinities. These affinities are of two sorts. One, by virtue of which the molecules of bodies adhere together, is known under the name of the affinity of aggregation, or attraction of cohesion ; this we have recently alluded to. The various degrees of this affinity govern the differences which are apparent in the resistance of bodies to ex ternal force. When it is considerable, the substances are hard and solid; when inconsiderable, they are liquid; and when this force is still more diminished, they become gaseous. These three states of bodies—the solid, liquid, and gaseous—are called forms of aggregation. On this affinity of aggregation depend also the regular forms which are assumed by certain bodies when they pass from the liquid to the solid state; this is known in chemistry by the word crystallization. Hardness, softness, toughness, brittle ness, &c., are equally dependent on this form of a force. Its powers may be mechanically overcome by pulverisation or similar operations, and chemically by the action of heat. The other kind of affinity is known under the name of affinity of composition, or chemical affinity. It is not only exercised in compound substances, between the simple bodies of which they are composed, but also between identical atoms which unite to form molecules. By its means two bodies are enabled to unite, and give rise to a third new substance, which frequently does not possess the inherent qualities of the substances of which it was compounded. Thus chlorine and silver are enabled, by means of their chemical affinity, to unite and form the white powder, chloride of silver. For this reason, it is customary, in describing the two kinds of affinity, to call the first—that of aggregation—a force exerted between homogenous substances; for example, between the separate molecules of chloride of silver; whilst the second— chemical affinity—is exerted between heterogeneous substances ; for instance, between chlorine of silver, and between elementary atoms, which form molecules by their union ; thus, H,, free hydrogen, and Ola, free chlorine. Heat, light, electricity, and other forms of force, possess the property of frequently sepa rating bodies held together by chemcal affinity. The whole art of photography is, indeed, based on the power of light to effect chemical decompositions. SOLID AND LIQUID ILLUMINATING AGENTS. BY LEOPOLD FIELD, F.C.S.* The introduction of lamps into Greece was gradual and slow. Probably, by the end of the 5th century b.c., they were in gene ral use in the upper ranks of society. Herodotus (ii. 62), writing of the Lychnohaie (feast of lamps) at Sais, in Egypt (450 B.o.), does not express surprise at the lamps themselves, but only at the great number thereof. Their lamp differed in no way from that of Rome ; the wick (epuaAA(s) made from the woolly leaves of an indigenous plant, passed through the nose IpvKT-fip) into the crude olive oil. Those who wish to become more intimately acquainted with the various styles of ornament in vogue among old nations will fi d every conceivable shape and size in the Etruscan Vase Gallery at the British Museum, to which 1 must beg to refer them for further illustration. Becker’s Galins and * Continued from page 493. Charicles also are replete with information on this point. I could not pursue the subject further, without trenching on the ground of my future lectures, in which the main subject will always be prefaced by an outline history of that branch. You will be surprised to find both our latter day inventions fore shadowed in extreme antiquity, and the imperfections of the dark ages maintained to a recent date. It is worthy of comment, in conclusion, how fire and light have ever been invested with celestial attributes, and reserved for divine worship. I need only instance the Caspian fire- worshippers, and the Persian monarchs, with their silver fire trays borne before them into battle. Great festivals of lamps have been common to all nations. The Lychnokaie, above- mentioned as an Egyptian lamp-feast, has its parallel in the Chinese feast of lanterns. We send out annually many thousand scarlet candles, lobchocks—here is one—for this festival, which happens on the fifteenth day of the first month. Then the Greeks had their Kap.aabn-bpop.'ia, and the Romans their Luper- calia. In lieu of this feast, remarkable for its licentiousness, Pope Gelasius instituted Candlemas, falling on the 2nd February. Some have it, that Vigilius supplanted the Proserpina by this festival. Anyhow, though the significance be changed, candles play the chief role in both. According to Pliny (Nat. Hist.), the Romans themselves used waxed candles in certain rites. I nee d scarcely hint at tbe eternal lamp of Vesta, tended by damsels of established reputation ; the never dying lights of Mahomet’s tomb, Aaron's tabernacle, and Roman Catholic churches. The Romans lighted lamps in honour of Prometheus, who caught fire from heaven; of Minerva, who gave them oil; of Vulcan, who invented lamps; birthdays were sometimes called days of lamps, as the bulk of their gifts took that form, in cheap terra cotta or costly metal; there was the fax belli or war torch, and fax nuptialis, the emblem of marriage. “ There let Hymen oft appear, In saffron robe, with taper clear.” Milton, (“Allegro”). On the tombs of the dead, lamps were placed by the sorrow ing hands of their legatees, filled with scented oil. An oracular statue of Hermes, in Achaia, was “ worked ” by lighting a lamp before him, and placing a small coin at his feet. Ingenious suggestions have been made about eternal lamps in tombs, which are positively averred to have been found burning after the lapse of centuries. “Our wasted oil unprofitably burns, Like hidden lamps in old sepnlchral urns.” Couper (“Conversation”). Indeed, Rosicrucius gives a description of his eternal lamp, with all the circumstance of discovery. “ But this,” says Disraeli, “is only dwelt on to make it appear that he did discover some thing.” Boyle undertook a series of experiments with the air- pump, which demonstrated the absurdity of such statements. Reserving my private opinion as somewhat iconoclastic, I might suggest the possibility of an asbestos wick, communicating with a supply of light naphtha, burning indefinitely in a tomb not absolutely air-tight. Possibly, also, highly carbonaceous vapours in the sepulchre might have been kindled by the intruded torch. After this hasty glimpse at our wretchedly illumined fore fathers, you will be more than ever inclined to endorse Lamb’s opinion, that “ one can never hear mention of them without an accom panying feeling, as though a palpable obscure had dimmed the face of things, and that our ancestors wandered to and fro— groping.” Adhering to the plan of commencing ab ovo, we will apply our selves in this lecture to the study of those substances which can be used for illumination in a crude manufactured form, or, rather, with unchanged chemical composition. Tallow, bees wax, and sperm-wax are the chief of such naturals, and we will discuss them accordingly. I have already referred to the distinction drawn by Apuleius between cerei and sebacei; also to the fact of wax candles having entered into certain rites of heathen worship. Partly from the smaller supply, chiefly though, no doubt, from the superiority of its appearance, hardness of grain, and sweeter odour, the wax candle has ever lorded it over the unsavoury tallow dip, associated with kitchen and garret, while the wax taper suggests cathedral and boudoir. In days before gas and Argand lamps, people’s rank was not unfrequently gauged by the class of candle they affected. “Wax candles in the schoolroom!” says Mrs. Elton, in “ Emma.” Lord Bacon, in his “Natural History, extols wax lights as lasting longer than tallow candles, because
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