Page:Popular Science Monthly Volume 6.djvu/575

Rh such a flame was discovered by Professor Le Conte in the United States, who had the sagacity to seize upon the most essential features of the phenomenon. A similar observation was subsequently made by Prof. Barrett, while assistant in the physical laboratory of the Royal Institution; and both he and myself, my present assistant Mr. Cottrell, and Mr. Philip Barry, have succeeded in pushing such flames to an extraordinary degree of sensitiveness. The following brief description of a sensitive flame 24 inches high, issuing from the single orifice of a steatite-burner, is taken from my forthcoming "Lectures on Sound:" "The slightest tap on a distant anvil causes it to fall to 7 inches. When a bunch of keys is shaken, the flame is violently agitated, and emits a loud roar. The dropping of a sixpence into a hand, already containing coin, knocks the flame down. The creaking of boots sets it in violent commotion. The crumpling or tearing of a bit of paper, or the rustle of a silk dress, does the same. Responsive to every tick of a watch held near it, it falls and explodes. The winding up of the watch produces tumult. From a distance of 30 yards we may chirrup to this flame, and cause it to fall and roar. Repeating a passage from the 'Faerie Queene,' the flame sifts and selects the manifold sounds of my voice, noticing some by a slight nod, others by a deeper bow, while to others it responds by violent agitation."

We are now prepared to understand a drawing and description of the apparatus first employed in the demonstration of aerial reflection. I take both drawing and description substantially from an account of the apparatus given by a writer in Nature, February 5, 1874:

"A tunnel t t' (Fig. 1), 2 inches square, 4 feet 8 inches long, open at both ends, and having a glass front, runs through the box, a b c d. The spaces above and below are divided into cells opening into the tunnel by transverse orifices exactly corresponding vertically. Each alternate cell of the upper series—the first, third, fifth, etc.—communicates by a bent tube (e e e) with a common upper reservoir (g), its counterpart cell in the lower series having a free outlet into the air. In like manner the second, fourth, sixth, etc., of the lower series of cells are connected by bent tubes (n n n) with the lower reservoir (i), each having its direct passage into the air through the cell immediately above it. The gas-distributors (g and i) are filled from both ends at the same time, the upper with carbonic-acid gas, the lower with coal-gas, by branches from their respective supply-pipes (f and h). A well-padded box (P) open to the end of the tunnel forms a little cavern, whence the sound-waves are sent forth by an electric bell (dotted in the figure). A few feet from the other end of the tunnel, and in a direct line with it, is a sensitive flame (k), provided with a funnel as sound-collector, and guarded from chance currents by a shade.

"The bell was set ringing. The flame, with quick response to