Fig. 3 shows the straight and outspread flame burner with a special heater.  In this arrangement the gas and air are heated before combustion, in the compartment, G, directly exposed to the action of a small Bunsen burner, R, which is placed (in an opaque glass) in the middle of a lyre-shaped figure formed by the two gas-pipes, AA.  The burner proper consists of two fine annular passages meeting above, and emitting a thin annular sheet of gas over the guide, T, made of a white refractory substance placed between the two annular jets.  The object of this guide is to stretch the incandescent sheet of flame, composed of several jets, and interpose friction, so as to prevent a too rapid ascent of hot gases.

[Illustration:  FIG. 3 and FIG. 4 REGENERATIVE BURNERS WITH INVERTED FLAMES.]

The luminous focus is placed within a glass globe, C, mounted on the bell, B, of the heater; and the external air enters this bell, mingling with the products of combustion of the heating burner, R. The portion, D, of the annular passage, B, being made of a highly conductive metal, the gas becomes heated in passing to the burner, so that both gas and air are raised to the same temperature by the time they reach the orifices of the burner.  Instead of prolonging the gas-pipe to the point of bifurcation, a chamber may be arranged immediately below the guide, for the gas and air to become intimately mixed by passing through several perforations or wire gauze, receiving the excess of heat from the white porcelain guide.  The admission of gas to both the main and heating burners is regulated by a double valve in the pipe; but this arrangement may be used without any previous heating of the gas and air.

Fig. 4 shows a similar arrangement to that above described, but reversed; the gas and air being previously heated by the products of combustion.  The two pipes, D, lead the gas to the burner; and the incandescent sheet of flame is drawn over a white refractory substance, having in its center an orifice through which the hot gases rise to the upper portion of the burner.  The luminous sheet is spread out all the better on account of this return of the flames, which also causes the mixture of air and gas to be more complete than when they rise directly.  The gas escapes horizontally from the orifices of the annular burner, B, and mingles with the double current of hot air which rushes in above the flame inside the globe, and also below through the central portion of the burner.

This lamp throws its light vertically downward; and its illuminating power may be increased by providing, above the incandescent sheet, a reflector, which diverts into a useful direction the rays thrown toward the ceiling.  In this arrangement of lamp the flame is excessively condensed by its being turned back over the refractory guide; and this condensation greatly favors the production of light.  On the other hand, the combustion of the gas is very perfect, because the currents of hot air are thrown directly upon the two sides of the flame; and thus the reciprocal action becomes more intense.  Lastly, the division of the gas into a large number of small jets, in contact with which the hot air forms an intimate mixture, causes a greater quantity of molecules to partake in the combinations; thus affording a proportionate increase of temperature in a given space and time.