The Silber Argand, which is a remarkably efficient burner, in the main features of its construction is very closely related to Mr. Sugg's later Argands just described. The air is directed on to the outer surface of the flame, as in those burners, by a curved deflector, of which the upper edge is, however, at a higher level than in Mr. Sugg's burners. Air is also admitted between the deflector and the glass chimney. The most striking divergence in its construction from that of Mr. Sugg's burners is contained within the opening in the centre of the burner. Instead of a solid metal spike, there is a brass tube, through which, as well as between its circumference and the cylindrical body of the burner, air can enter to feed the inner surface of the flame. In addition to promoting the steadiness of the flame, it would appear that the air entering through this inner tube supports the combustion of the gas at the tail of the flame. The arrangements for diminishing the pressure of the gas within the burner, and for ensuring its equable distribution to all parts of the ring of holes, though quite different, seem to be scarcely less complete than those employed in the "London" burner. From the nipple which connects the burner to the gas supply, the gas enters (by four minute perforations) into a horizontal chamber, where its velocity is checked, and whence it is conveyed into the cylindrical chamber forming the main body of the burner. The very satisfactory performances of the burner (which are in advance of those of the standard Argand) sufficiently attest the correctness of its construction. [Sidenote: Multiple Argands.] For consuming large quantities of gas, double or treble Argands are constructed. These consist, in effect, of two or three Argand burners placed concentrically to each other within one chimney. Mr. Sugg has produced a series of burners of this class, designed to pass quantities of gas ranging from 15 to 55 cubic feet per hour; and, in some instances, exceeding even the latter figure. These burners, with ordinary (16-candle) coal gas, give a light equal to 4 candles per cubic foot of gas consumed; which is a considerably better result than is afforded by the standard burner. The cause of their yielding results so superior to the ordinary Argand is found in the circumstance that their flames present a much smaller surface area to the cooling action of the air, in proportion to the quantity of gas consumed. The arrangement of these burners differs from that of the improved single Argands, which have been described, only in that there are two or more steatite cylinders, each fed by its own supply-tubes, and having its own distinct ring of holes; while the space between the cylinders is so proportioned as to admit no more than the quantity of air required to produce the necessary intensity of combustion. [Illustration: FIG. 15.--THE DOUGLASS ARGAND. (_A A, Focal Plane, or Belt of Strongest Light._)]