LIGHTS, ARTIFICIAL. Most kinds of artificial light, for domestic and manufacturing purposes, are produced by the combustion of coal, solid tallow, liquid oil, or some sort of spirit. One special kind, due to the action of an 'electric current on charcoal, is described under ELECTRIC LICHT ; another, produced by the action of oxyhydrogen gas on lime, is treated under DRUMMOND LICHT ; a third, of which the peculiarities are due rather to the apparatus than to the combustible substances, noticed under LAMP, SAFETY; while gas-lights are fully treated in the articles Gas, Maritisecronn or ; and Ges-Licuerizio.
Candles.—These, in the different varieties of dip tallow, moulded tallow, wax, palm oil, composite, stearin°, &c., are described in their nature and production under CA..NDLE MANUFACTURE. We may here simply notice the Soho lamp, patented a few years ago, for burning solid tallow or some other kind of fat. The tallow is brought to the form of a long cylinder like a candle without a wick, and is placed in the vertical stem of the lamp ; there is a spiral spring beneath it, which presses it up close to a conical cap or cover at the top. A fixed tube passes up through- the centre of the cylinder of tallow, from top to bottom ; and in this tube is placed a cotton wick dipped in wax, the height of which above the top of the tallow can be regulated by a rack, pinion, and nut. The tallow or fat is made into a hollow cylinder in order to leave room for the central tube containing the wick. When the lamp is to be extinguished, the wick is drawn down below the top of the tube, and again raised before the tallow becomes cold.
One of the projects of this class consists in placing any kind of wax or tallow or fat in a receptacle, having either hot water or hot metal beneath it, so as to keep it in a melted state, fitted to be used in the same manner as oil ; but any method of keeping the water or the metal hot would seem likely to be a, far greater inconvenience than any supposed good arising from the use of a solid food for the lamp. In another contrivance, however, where the substance employed is either lard or tallow, there is a piece of metal which descends from the flame into the vessel containing the lard ; and this metal, becoming heated by the flame, communicates this heat to the lard, and thus keeps it in a melted state. The inconvenience of such arrangements arises frOm the circumstance that the hot water or a heated piece of metal must be put into the lamp before lighting it, in order to melt the tallow. When this preliminary step is taken, the tallow is kept in a melted state by various means. One ingenious mode consists in having an air-tube within the wick, to carry air up to the flame, and two projections from this tube penetrating into the flame itself ; so that the metal of which the tube is made, becoming heated at the upper end, speedily communicates heat to the contents of the lamp below.
Bode Light.—As something intermediate between gas-light and oil light, we may notice the Bude light, devised and named by Mr. Golds
worthy Gurney. Originally the light was obtained from an oil-lamp, the flame from which was acted on by a current of oxygen gas : sub sequently oil-gas was substituted for the liquid oil ; but afterwards the gas which is made for lighting the streets of towns was employed to produce the flame, the brilliancy being increased by a current of atmo spherical air ingeniously introduced. The apparatus being suspended from the ceiling, the gas, either as it comes from the street or purified by chemical processes, passes up a number of short tubes into con centric annular receivers, the upper surfaces of which are pierced on the whole of their circumference with small holes. On issuing from the perforations the gas- is ignited, and thus there are formed as many cylinders of flame as there are rings ; while between and around the several cylinders the atmospheric air rises from below to support the combustion. A hollow frustum of a cone, of glass, open at both extremities and having its larger end downwards, surrounds the tubes above mentioned ; its lower part resting on the base of the framework within which they are suspended, and its upper part approaching very near the bottom of the flame, so that the atmospheric air in rising is confined between the upper or smaller end of the cone and the flame. The distances between the cone and the rings, and between the rings themselves, are regulated by experiment so that the quantity of air may suffice to bring the temperature of the gas to exactly the degree necessary for causing a separation of the charcoal from the flame, as nearly as possible at the moment that the latter issues from the perforations. The flame from each interior ring serves to augment the heat of that which is on the exterior of it, by which means an increased intensity of light in each is produced ; and almost the whole of the light that emanates from the interior rings passes through the flame on its exterior, into the apartment. A cylindrical glass chimney rests at its lower extremity on the margin of a circular aperture in the middle of a circular disk of iron, from 18 inches to 2 feet in diameter, the under surface of which serves as a reflector : this disk, and with it the chimney, is capable of being raised or lowered, by Means of adjusting screws, till it conceals the upper extremities of the flame ; and thus the latter presents the appearance of a brilliant zone of white light, which is from 3 inches to 6 inches high, according to the pressure of the gas. An apparatus of this kind supersedes the employment of many separate lamps; and, being placed at a consider able height from the floor, it is possible to apply above the glass chimney a pipe which, while it conveys the impure products of combustion through the ceiling, may serve to ventilate the building or apartment. This is found to be a cheap mode of producing a bright light ; but as a similar effect may be produced by. other means, the distinctive name of Buda light is not now much employed.