ch is decked over and fitted with a framework of
3-inch angle-iron 9 feet high, to which a 300-pound bell is rigidly
attached. A radial grooved iron plate is made fast to the frame under the
bell and close to it, on which is laid a free cannon-ball. As the buoy
rolls on the sea, this ball rolls on the plate, striking some side of the
bell at each motion with such force as to cause it to toll. Like the
whistling-buoy, the bell-buoy sounds the loudest when the sea is the
roughest, but the bell-buoy is adapted to shoal water, where the
whistling-buoy could not ride; and, if there is any motion to the sea, the
bell-buoy will make some sound. Hence the whistling-buoy is used in
roadsteads and the open sea, while the bell-buoy is preferred in harbors,
rivers, and the like, where the sound-range needed is shorter, and
smoother water usually obtains. In July, 1883, there were 24 of these
bell-buoys in United States waters. They cost, with their fitments and
moorings, about $1,000 each.

_Locomotive-Whistles._--It appears from the evidence given in 1845, before
the select committee raised by the English House of Commons, that the use
of the locomotive-whistle as a fog-signal was first suggested by Mr. A.
Gordon, C.E., who proposed to use air or steam for sounding it, and to
place it in the focus of a reflector, or a group of reflectors, to
concentrate its sounds into a powerful phonic beam. It was his idea that
the sharpness or shrillness of the whistle constituted its chief value.
And it is conceded that Mr. C.L. Daboll, under the direction of Prof.
Henry, and at the instance of the United States Lighthouse Board, first
practically used it as a fog-signal by erecting one for use at Beaver Tail
Point, in Narragansett Bay. The sounding of the whistle is well described
by Price-Edwards, a noted English lighthouse engineer, "as caused by the
vibration of the column of air contained within the bell or dome, the
vibration being set up by the impact of a current of steam or air at a
high pressure." It is probable that the metal of the bell is likewise set
in vibration, and gives to the sound its timbre or quality. It is noted
that the energy so excited expends its chief force in the immediate
vicinity of its source, and may be regarded, therefore, as to some extent
wasted. The sound of the whistle, moreover, is diffused equally on all
sides. These characteristics to some extent explain the impotency of the
sound to penetrate to great d