a vessel containing oil, with a lighted wick. Lamps were in general use amongst the Jews, Greeks, and Romans. The candlestick with seven branches, placed in the sanctuary by Moses, and those which Solomon afterwards prepared for the temple, were crystal lamps filled with oil, and fixed upon the branches. The lamps or candlesticks made use of by the Jews in their own houses were generally put into a very high stand on the ground. The lamps supposed to be used by the foolish virgins, &c. in the gospel, were of a different kind.—According to critics and antiquaries, they were a sort of torches, made of iron or potter's earth, wrapped about with old linen, and moistened from time to time with oil. Matth. xxv. The lamps of Gideon's soldiers were of the same kind. The use of wax was not unknown to the Romans, but they generally burnt lamps; hence the proverb *Tempus et oleum perdidi*, "I have lost my labour." Lamps were sometimes burnt in honour of the dead, both by Greeks and Romans.

Dr St Clair, in the Philos. Transf. n° 245, gives the description of an improvement on the common lamp. He proposes that it should be made two or three inches deep, with a pipe coming from the bottom almost as high as the top of the vessel. Let it be filled so high with water that it may cover the hole of the pipe at the bottom, that the oil may not get in at the pipe and so be lost. Then let the oil be poured in so as to fill the vessel almost brim-full; and to the vessel must be adapted a cover having as many holes as there are to be wicks. When the vessel is filled and the wicks lighted, if water falls in by drops at the pipe, it will always keep the oil at the same height or very near it; the weight of the water being to that of the oil as \(20\frac{1}{3}\) to \(19\), which in two or three inches makes no great difference. If the water runs faster than the oil wastes, it will only run over at the top of the pipe, and what does not run over will come under the oil, and keep it at the same height.

From experiments made in order to ascertain the expense of burning chamber oil in lamps, it appears, that a taper lamp, with eight threads of cotton in the wick, consumes in one hour \(\frac{1}{3}\frac{3}{5}\) oz. of spermaceti oil, at 28. 6d. per gallon; so that the expense of burning 12 hours is 4.57 farthings. This lamp gives as good a light as the candles of eight and ten in the pound; it seldom wants snuffing, and casts a strong and steady light. A taper, chamber, or watch lamp, with four ordinary threads of cotton in the wick, consumes 0.1664 oz. of spermaceti oil in one hour; the oil at 28. 6d. per gallon, makes the expense of burning 12 hours only 2.34 farthings.

**Perpetual Lamps.** The testimonies of Pliny, St Austin, and others, have led many to believe that the ancients had the invention of perpetual lamps; and some moderns have attempted to find out the secret, but hitherto in vain. Indeed it seems no easy matter to find out either a perpetual wick or a perpetual oil. The curious may read Dr Plot's conjectures on the subject in the Philos. Transf. n° 166; or in Lowthorp's abridgment, vol. iii. p. 636. But few, we believe, will give themselves the trouble of searching for the secret, when they consider that the credulity of Pliny and of St Austin was such, that their testimony does not seem a sufficient inducement to us to believe that a lamp was ever formed to burn 1500 or 1000 years: much less is it credible that the ancients had the secret of making one burn for ever.

**Rolling Lamp:** A machine A B, with two moveable circles D E, F G, within it; whose common centre of motion and gravity is at K, where their axes of motion cross one another. If the lamp K C, made pretty heavy and moveable about its axis H I, and whose centre of gravity is at C, be fitted within the inner circle, the common centre of gravity of the whole machine will fall between K and C; and by reason of the pivots A, B, D, E, H, I, will be always at liberty to descend; hence, though the whole machine be rolled along the ground, or moved in any manner, the flame will always be uppermost, and the oil cannot spill.

It is in this manner they hang the compasses at sea; and thus should all the moon-lanterns be made, that are carried before coaches, chaises, and the like.

**Argand's Lamp.** This is a very ingenious contrivance, and the greatest improvement in lamps that has yet been made. It is the invention of a citizen of Geneva; and the principle on which the superiority of the lamp depends, is the admission of a larger quantity of air to the flame than can be done in the common way. This is accomplished by making the wick of a circular form; by which means a current of air rushes through the cylinder on which it is placed with great force; and, along with that which has access to the outside, excites the flame to such a degree that the smoke is entirely consumed. Thus both the light and heat are prodigiously increased, at the same time that there is a very considerable saving in the expense of oil, the consumption of the phlogiston being exceedingly augmented by the quantity of air admitted to the flame; so that what in common lamps is dissipated in smoke is here converted into a brilliant flame.

This lamp is now very much in use; and is applied not only to the ordinary purposes of illumination, but also to that of a lamp furnace for chemical operations, in which it is found to exceed every other contrivance yet invented. It consists of two parts, viz. a reservoir for the oil, and the lamp itself. The reservoir is usually in the form of a vase, and has the lamp proceeding from its side. The latter consists of an upright metallic tube about one inch and five-tenths in diameter, three inches in length, and open at both ends. Within this is another tube about an inch in diameter, and nearly of an equal length; the space betwixt the two being left clear for the passage of the air. The internal tube is closed at the bottom, and contains another similar tube about half an inch in diameter, which is soldered to the bottom of the second. It is perforated throughout, so as to admit a current of air to pass through it; and the oil is contained in the space betwixt the tube and that which surrounds it. A particular kind of cotton cloth is used for the wick, the longitudinal threads of which are much thicker than the others, and which nearly fills the space into which the oil flows; and the mechanism of the lamp is such, that the wick may be raised or depressed at pleasure. When the lamp is lighted, the flame is in the form of a hollow cylinder; and, by reason of the strong influx of air through the heated metallic tube, becomes extremely bright, the smoke being entirely consumed for the reasons already mentioned. The heat and light are still farther increased, by putting over the whole a glass cylinder nearly of the size of the exterior tube. By diminishing the central aperture, the heat and light are proportionably diminished, and the lamp begins to smoke. The access of air both to the external and internal surfaces of the flame is indeed so very necessary, that a sensible difference is perceived when the hand is held even at the distance of an inch below the lower aperture of the cylinder; and there is also a certain length of wick at which the effect of the lamp is strongest. If the wick be very short, the flame, though white and brilliant, emits a disagreeable and pale kind of light; and if very long, the upper part becomes brown, and smoke is emitted.

The saving of expense in the use of this instrument for common purposes is very considerable. By some experiments it appears that the lamp will continue to burn three hours for the value of one penny; and the following was the result of the comparison between the light emitted by it and that of a candle. The latter having been snuffed to burn so long without snuffing, that large lumps of coaly matter were formed upon the wick, gave a light at 24 inches distance equal to the lamp at 129 inches; whence it appeared that the light of the lamp was equal to 28 candles in this state. On snuffing the candle, however, its light was so much augmented, that it became necessary to remove it to the distance of 67 inches before its light became equal to that of the lamp at 129 inches; whence it was concluded that the light of the lamp was somewhat less than that of four candles fresh snuffed. At another trial, in which the lamp was placed at the distance of 13½ inches, and a candle at the distance of 55 inches, the lights were equal. In these experiments the candles made use of were 10½ inches long, and 2½ inches in diameter. When the candle was newly snuffed, it appeared to have the advantage; but the lamp soon got the superiority; and on the whole it was concluded, that the lamp is at least equivalent to half a dozen of tallow candles of six in the pound; the expense of the one being only two pence haltpenny, and the other eight pence in seven hours.

The best method of comparing the two lights together seems to be the following. Place the greater light at a considerable distance from a white paper, the smaller one being brought nearer or removed farther off as occasion requires. If an angular body be held before the paper, it will project two shadows: these two shadows can coincide only in part; and their angular extremities will, in all positions but one, be at some distance from each other; and being made to coincide in a certain part of their bulk, they will be bordered by a lighter shadow, occasioned by the exclusion of the light from each of the two luminous bodies respectively. These lighter shadows, in fact, are spaces of the white paper illuminated by the different luminous bodies, and may easily be compared together, because at a certain point they actually touch one another. If the space illuminated by the smaller light appear brightest, the light must be removed farther off, but the contrary if it appear more obscure.

On cutting open one of Argand's wicks longitudinally, and thus reducing the circular flame to a straight lined one, the lights appeared quite equal in power; but the circular one had by far the greatest effect in dazzling the eyes; though when the long flame was made to shine on the paper, not by the broadside, but in the direction of its length, it appeared more dazzling than the other. On placing this long flame at right angles to the ray of Argand's lamp, it projected no shadow; but when its length was placed in the direction of the ray, it gave a shadow bordered with two broad, well defined, and bright lines.

The broad-wicked lamp seems to have the advantage of the other, as requiring less apparatus; and indeed by this contrivance we may at the most trifling expense have a lamp capable of giving any degree of light we please. The only disadvantage attending either the Lampadary one or the other is, that they cannot easily be carried from one place to another; and in this respect it does not seem possible by any means to bring lamps to an equality with candles.

Lamp-Black, among colourmen. See Colour-Making, n° 18, 19.—Substances painted with lamp-black and oil, are found to resist the effects of electricity to a surprising degree; so that in many cases even lightning itself seems to have been repelled by them. See Lightning; Thunder; Chemistry, n° 700. and Electricity, p. 478. col. 1.