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._
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