SOUND.
The difficulty of transmitting sounds to a great distance arises from the sound spreading and losing itself in the surrounding air; so that if we could confine it on one side, as along a well—on two sides, as in a narrow street—or on all sides, as in a tube or pipe—we should be able to convey it to great distances. In the cast-iron water-pipe of Paris, which formed a continuous tube with only two bendings near its middle, the lowest whisper at one end was distinctly heard at the other, through a distance of 3,120 feet. A pistol fired at one end actually blew out a candle at the other end, and drove out light substances with great violence. Hence we see the operation of speaking tubes which pass from one part of a building to another, and of the new kind of bell which is formed of a wooden or tin tube, with a small piston at each end. By pushing in one piston, the air in the tube conveys the effect to the piston at the other end, which strikes against the bell—this piston being, as it were, the clapper on the outside of the bell. The intensity of confined sounds is finely exhibited at Carisbrook Castle, in the Isle of Wight. There is here a well 210 feet deep, of twelve feet in diameter, and lined with smooth masonry; and when a pin is dropped into it, the sound of its striking the surface of the water is distinctly heard.—Ibid.