188 Editorial Miscellany. 



Other observations demonstrated the existence of acoustic clouds, 

 lining the optically transparent atmosphere, and causing distinct 

 echoes of great intensity and long duration, to which the rolling of 

 thunder is to be ascribed. 



" But the strength of science," says Prof, Tyndall, " consists in veri- 

 fication, and I was anxious to submit the question of aerial reflection 

 to an experimental test. As in most similar cases, it was not tlie sim- 

 plest cond)inations that were first adopted. Two gases of different 

 densities were to be chosen, and I chose carbonic acid and coal gas. 

 With the aid of my skillful assistant, Mr. John Cottrel, a tunnel was 

 formed, across which five-and-twenty layers of carbonic acid were per- 

 mitted to fall, and five-and-twenty alternate layers of coal gas to rise. 

 Sound was sent through this tunnel, making fifty passages from 

 medium to medium in its course. These, I thought, would waste in 

 aerial echoes a sensible portion of sound. 



" To indicate this waste an objective test was found in a gas-flame 

 brought to the vei-ge of flaring. The action of sonorous vibrations on 

 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 seven 

 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 crumbling 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 thirty 

 yards we may chirrup to this flame, and cause it to fall and roar. 

 Repeating a passage from the ' Faerie Q.ueene,' 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." 



The exceedingly interesting experiments which are detailed, relate 

 to the action of layers of air, saturated with the vapors of various 

 volatile liquids, in the transmission of sound. 



