LAM 



LAM 



LAMINAE, the thin plates of which 

 any thing consists : hence the epithet 

 laminated, which is applied to those 

 bodies whose texture discovers such a 

 disposition as that of plates lying over 

 one another. 



LAAIIUM, in botany, archangel, a ge- 

 nus of the Didynumia Gymnospermia 

 class and order. Natural order of Ver- 

 ticiiiatx. Labiate, Jussieu. Essential 

 character : corolla upper lip entire, vault- 

 ed ; lower, two-lobed ; throat with a re- 

 flex toothlet on each side. There are 

 thirteen species, several of which are 

 considered as weeds, ratiier than garden 

 plants. The L. album, white archangel, 

 or dead nettle, is common in hedges, on 

 banks, and byroad-sides; flowering in 

 April and May, when it is much resorted 

 to by bees, for the honey secreted in the 

 bottom of the tube, by the gland that 

 surrounds the 'base of the germ. Tin's 

 plant has a disagreeable smell when 

 bruised. I'haljena Chrysitis, or bnrnish- 

 ed-brass moth, feeds on it : Linn<eus says, 

 the leaves are eaten in Sweden as a pot- 

 herb, in the spring; no cattle, however, 

 seen 1 , to touciiit; and, having a strong, 

 creeping, perennial root, it should be ex- 

 tirpated, which is not difficult. 



LA M P, * li-gantrs. 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 wilh 

 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 

 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 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 proporiiuuably 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 bejovv 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 



