Fig. 8 shows a double flame burner on the principle of Mr. Heron's, but with admission of hot air into the angle formed by the flames. As exemplified by Mr. Heron, if two equal batswing burners separately give a certain amount of light, on the two flames being brought into contact, so as to form a single flame, the luminosity is considerably increased, owing to the condensation of heat which results from their meeting. The two incandescent sheets are, as it were, forced into one another, so as to be combined. [Illustration: FIG. 8. DOUBLE FLAT-FLAME BURNER] The high-power burners of Douglass, Coze, Mallet, and others were designed on this principle; but its application to uninclosed burners was not very satisfactory, because the great cooling down of the inner surface of the flames by the strong draught of cold air impaired their illuminating power. To counteract this difficulty, M. Somzee adopts a heating burner, A, which he places between the two batswing burners, B, so that the products of combustion rise in the angle made by the two lighting flames, as shown; thus greatly increasing their luminosity while maintaining a low consumption of gas. M. Somzee also raises the illuminating power of an ordinary flat-flame burner by causing an obscure effluvium to traverse the dark portion of the flame. The effect of this is to increase the activity of decomposition in this portion, so that the particles of carbon are the more readily set free, and remain longer in suspension in the luminous zone. The obscure effluvium may be determined between two points by the electric current, or be caused by the heating of an imperfect conductor by the current; or, again, it may result from a metal conductor heated by the reactions produced in the middle of the flame, by separating the cone of matter in ignition. The effect may be compared with that obtained by the concentration of two sheets of flame; but in this case the sheets are formed by the constituent parts of one and the same flame, whence results a more complete utilization of the elements composing it. This system is, in fact, a simplification of the arrangement adopted in the double-flame burner seen in Fig. 8. Fig. 9 shows a reflecting and regenerative burner with double glass. The crown, made of metal polished on both sides, has a circular groove, G, for receiving the end of the central chimney, C, and presenting an annular aperture by which the products of combustion enter. The second glass, C¹, is fastened to the collar of the burner carrier, and does not come into contact with the metal crown; so as to allow the air to enter from outside for supplying the burner. The gas enters by the pipe, T, provided with a cock. This pipe is continued to the top of the apparatus, and there spreads out into the form of a dome; thus dividing into two compartments the trunconic chamber, S¹ S squared, whence the hot gas returns to the body of the burner, B.