DRUMMOND LIGHT, or LIGHT. The heat given out during the combus tion of a mixture of hydrogen and oxygen gases, or of coal-gas and oxygen, is very intense; and when the mixture is directed on an infusible substance such as lime, a most brilliant light is evolved. Capt. Drummond, R.E., originally proposed the employment of this light in the trigonometrical survey of Great Britain, and constructed apparatus for its production. Sec DRUMMOND, THOMAS. In the most convenient form of the apparatus the mixed gases escaping by a jet, being set fire to and made to impinge upon a cylinder of lime, raise the surface of the latter nearest the jet to a white heat, accom panied by a dazzling light. As minute portions of lime become detached and are volatilized from the spot on the lime on which the jet of burning gases strikes, it is necessary to expose a new surface of lime to the gases, and for this purpose a screw may be turned by the hand or by clockwork. The hydrogen and oxygen ought to be confined in separate gas-holders or bags, and to be brought by different tubes, provided with separate stop-cocks, to within a short distance of the exitjet. The common tube through which the mingled gases pass to the jet is about 6 in. long by two thirds of an inch in diameter; and in Mr. Hemming's construction the tube is very closely packed, full
of very fine brass wire, which is afterwards wedged in by a stout wire being driven down the center. The object of the fine wires is to prevent the return of the flame, which might lead to a disastrous explosion. When the rays from this light are concen trated by a parabolic reflector, it can be seen at immense distances. Thus, on the 31st Dec., 1845, at half-past 3 P.M. (daylight), the light was exhibited on the top of Slieve Donard, in county Down, and was seen from the top of Snowdon, a distance of 108 m. ; and in other instances the D. L. has been seen at distances up to 112 miles. The em ployment of coal-gas instead of hydrogen has greatly increased the applications of the D. L., and it is now often used in magic-lanterns and other apparatus where great brilliancy and penetration of light are required. It has been used lately on the continent with great effect in illuminations. Great caution should at all times be exercised in the preparation, storing, and employment of the gases, as many dangerous explosions have occurred. Little heat is evolved from the D. L., nor does it vitiate the surrounding air, or consume its oxygen.