A notable advance in the synthesis of corundum, particularly of ruby, was made in 1904, when Verneuil, who had served his apprenticeship to science under the guidance of Frémy, invented his ingenious inverted form of blowpipe (Fig. 53), which enabled him to overcome the difficulties that had baffled earlier investigators, and to manufacture rubies vying in appearance after cutting with the best of nature’s productions. The blowpipe consisted of two tubes, of which the upper, _E_, wide above, was constricted below, and passing down the centre of the lower, _F_, terminated just above the orifice of the latter in a fine nozzle. Oxygen was admitted at _C_ through the plate covering the upper end of the tube, _E_. A rod, which passed through a rubber collar in the same plate, supported inside the tube, _E_, a vessel, _D_, and at the upper end terminated in a small plate, on which was fixed a disc, _B_. The hammer, _A_, when lifted by the action of an electromagnet and released, fell by gravity and struck the disc. The latter could be turned about a horizontal axis placed eccentrically, so that the height through which the hammer fell and the consequent force of the blow could be regulated. The rubber collar, which was perfectly gas-tight, held the rod securely, but allowed the shocks to be transmitted to the vessel, _D_, an arrangement of guides maintaining the slight motion of the vessel strictly vertical. This vessel, which carried the alumina powder used in the manufacture of the stone, had as its base a cylindrical sieve of fine mesh. The succession of rapid taps of the hammer caused a regular feed of powder down the tube, the amount being regulated by varying the height through which the hammer fell. Hydrogen or coal-gas was admitted at _G_ into the outer tube, _F_, and in the usual way met the oxygen just above the orifice, _L_. To exclude irregular draughts, the flame was surrounded by a screen, _M_, which was provided with a mica window, and a water-jacket, _K_, protected the upper part of the apparatus from excessive heating. [Illustration: FIG. 54.—‘Boule,’ or Pear-shaped Drop.]