LAMP, a vessel containing oil, with a lighted wick. Dr St Clair, in the Philos. Trans. no 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 20th 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 expence of burning chamber-oil in lamps, it appears, that a taper-lamp, with eight threads of cotton in the wick, consumes in one hour 1lb 5oz of spermaceti oil, at 2s. 6d. per gallon; so that the expence 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 2s. 6d. per gallon, makes the expence 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. Trans. no 166; or in Lowthorp's abridgement, 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.