LAMP, Argand's. This is a very inge nious contrivance, and the greatest im provement 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 very con siderable saving in the expense of oil, the combustion being exceedingly aug mented by the quantity of air admitted to the flame ; and that what in common lamps is dissipated in smoke is here con verted into a brilliant flame: This lamp is now very much in use ; and is applied not only to the ordinary purposes of illu mination, but also to that of a lamp fur nace for chemical operations, in which it is found to exceed every other contriv ance 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 pro ceeding from its side. The latter con sists of an upright metallic tube, about one inch and six-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 bot tom, and contains another similar tube, about half an inch in diameter, which is solderedto 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 be comes extremely bright, the smoke be ing 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 di minishing the central aperture, the heat and light are proportionably diminished, and the lamp begins to smoke. The ac, cess of air both to the external and inter nal 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 ex pense 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 fol lowing was the result of the comparison between the light emitted by it and that of a candle. The latter having been suf fered 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 lanip was equal to 28 can dles in this state. On snuffing the can dle, however, its light was so much aug mented; that it became necessary to re move it to the distance of 67 inches, be fore its light became equal to that of the lamp at 129 inches : whence it was con cluded, that the light ofthe lamp was some what less than that of four candles fresh snuffed. At another trial; in which the lamp was placed at the distance of 131.1 inches, and a candle at the distance of 55 inches, the lights were equal. In these experiments the candles made use of were 10i1 inches long, and inches in diameter. When the candle was newly snuffed it appeared to have the advan tage ; but the lamp soon got the supe riority; and on the whole it was conclud ed, that the lamp is at least equivalent to half a dozen of tallow candles, of six in the pound ; the expense of the one be ing only 21d. and the other 8d. in seven hours:.