Fig. 8. and 9. represent Lord Cochrane's patent lamp, which possesses all the advantages without any of the de fects of the common lamp. The glass vase N is made of a hemispherical figure, and the light is placed in the cen tre, so that the rays pass through the glass perpendicular to its surface. The top of the vase is covered up by a close cover K, from the centre of which a chimney L rises up nearly to the top of the roof or head AI, and terminates be neath the openings at the top of the same, where the smoke and heated air issue. To supply the lamp with fresh air, a curved tubef is carried beneath the oil reservoir e, and sup plies a constant current of fresh air to the flame, which is situated just between the orifices, or mouths, at the extre mity of the air pipe f, one being on each side of the wick, so that they project the air immediately upon the flame. The heated air, which is contained in the chimney L. can not balance the cool atmospheric air which enters freely through the air-pipe f, and rushing by the flame, displaces the hot air ; but, becoming heated, it will be forced up the chimney by the fresh air which follows through the air-pipe. By this means a most brilliant flame is kept up. That as little possible may be lost, the oil-vessel e is made very narrow, and the light which is thrown upwards to the cover K, is reflected downwards again on the pavement. The head, or roof AI of the lamp. is made with holes all round the lower edge to admit fresh air, and has also an opening in the top to allow the hot air to pass out; but both the air pipe e, and the chimney L, are open to the chamber or space within the head NI, and the consequence is, that the flame is never disturbed by winds, because, by the blowing of the wind, the air in the chamber KL is ren dered more dense, it will increase the pressure equally upon the orifice of the chimney L, and upon that or the air pipe e, so that the two actions will be balanced.
For the convenience of trimming and lighting this lamp, the roof NI is made to take off, but not the cover K. The chimney L is not fastened to the cover, but to a piece which lays upon it : this piece being lifted up, as shewn in Fig. 9. will rise upon a joint, or hinge, at a. and the oil vessel c, being suspended on the same joint, will be turned up like wise, so that the part containing the wick will rise up through a hole in the centre of the cover into a convenient situation for lighting the wick or replacing the cotton, as seen in Fig. 9. The oil vessel e is of the fountain kind; and when it is raised up in this way, the hole, or orifice for the admission of air, will be higher than the vessel, so that the oil can be poured in ; but when the oil vessel is restored to its proper situation, as in Fig. S. this hole will be immersed beneath the surface of the oil in the little cup which con tains the burner, so that it can only afford the oil as fast as it is consumed. Lord Cochrane has two patents for these
lamps, taken out in 1813, and they are used to great ad vantage in some districts in London. (J. F.) A very neat improvement upon the lamp has lately been introduced into this country from France. The oil is con tained in a circular rim, in the centre of which is placed the burner, which is supported upon a vertical stand. This circular rim is supported by two slender arms, proceeding to the stand ; and as the rim answers the purpose of a sup port for a hemispherical shade of paper on ground glass, the lamp has tile appearance of being supplied with its oil, either hydrostatically or mechanically, from the lower part of the stand.
It would be foreign to the present article to enter into any account of the recent and beautiful discoveries of Sir Davy, respecting flame and combustion, or to describe the ingenious safety lamps which he has invented. There is one invention, however, which has arisen from these discoveries, namely, a lamp without flame, which we shall here describe, as it may be of great use even for domestic purposes. If a cylindrical coil of thin platina wire, about the hundredth of an inch in diameter, is placed so that part of it surrounds the cotton wick of a spiral lamp, and part of it is above the wick, and if the lamp is lighted so as to heat the wire to redness ; then if the flame is blown out, the vapour which ascends from the alcohol will keep the upper part of the wire red hot, as long as there is any alcohol remaining in the lamp. This red hot coil of wire is capable of kindling German fungus, or paper prepared with nitre, so that a sulphur match, &c. may be at any time lighted. It is of great importance that the wire should be as nearly as possible the 100dtb of an inch in diameter, as a wire of a larger size yields only a dull red light, and a smaller one is very difficult to use. About 12 turns of the wire coiled round a cylindrical body, a little larger than the diameter of the wick, will be suffi cient. Four or five coils should be placed on the wick, and the remaining seven or eight coils above it. 'Mr. Thomas Gill, who has been the first to give a description of this lamp, found, by experiment, that a wick, composed of 12 threads, of the ordinary sized lamp cotton yarn, with the platina wire coiled round it, will require half an ounce of alcohol to keep it red hot for eight hours. During the ignition of the lamp, a slightly acid smell is given out, arising from the decomposition of the alcohol. This lamp has in one case been kept burning fur upwards of sixty hours. Mr. Gill used it for several nights in his bed-room with great convenience, and we have no doubt that it will not only come into general use as a night lamp for domes tic purposes, but will be of some utility in the arts. See the Annals of Philosophy for March 1818 vol. xi. p. 217.