THE ATMOSPHERE AND FOG-SIGNALING. 557 



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 agi- 

 tated, 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 se- 

 lects the manifold sounds of my voice, noticing some by a slight nod, 

 others by a deeper bow, while to others it responds by violent agita- 

 tion." 



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 1 1' (Fig. 1), 2 inches square, 4 feet 8 inches long, open 

 at both ends, and having a glass front, runs through the box, abed. 

 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. communi- 

 cates by a bent tube (e e e) with a common upper reservoir (#), 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 (/ 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 (&), 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 



