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 distances.  Difference in pitch is obtained by altering the distance between the steam orifice and the rim of the drum.  When brought close to each other, say within half an inch, the sound produced is very shrill, but it becomes deeper as the space between the rim and the steam or air orifice is increased.

Prof.  Henry says the sound of the whistle is distributed horizontally.  It is, however, much stronger in the plane containing the lower edge of the bell than on either side of this plane.  Thus, if the whistle is standing upright in the ordinary position, its sound is more distinct in a horizontal plane passing through the whistle than above it or below it.

The steam fog-whistle is the same instrument ordinarily used on steamboats and locomotives.  It is from 6 to 18 inches in diameter, and is operated by steam under a pressure of from 50 to 100 pounds.  An engine takes its steam from the same boiler, and by an automatic arrangement shuts off and turns on the steam by opening and closing its valves at determined times.  The machinery is simple, the piston-pressure is light, and the engine requires no more skilled attention than does an ordinary station-engine.

“The experiments made by the Trinity House in 1873-74 seem to show,” Price-Edwards says, “that the sound of the most powerful whistle, whether blown by steam or hot air, was generally inferior to the sound yielded by other instruments,” and consequently no steps were taken to extend their use in Great Britain, where several were then in operation.  In Canadian waters, however, a better result seems to have been obtained, as the Deputy Minister of Marine and Fisheries, in his annual report for 1872, summarizes the action of the whistles in use there, from which it appears that they have been heard at distances varying with their diameter from 3 to 25 miles.

The result of the experiments made by Prof.  Henry and Gen. Duane for the United States Lighthouse Board, reported in 1874, goes to show that the steam-whistle could be heard far enough for practical uses in many positions.  Prof.  Henry found that he could hear a 6-inch whistle 71/4 miles with a feeble opposing wind.  Gen. Duane heard the 10-inch whistle at Cape Elizabeth at his house in Portland, Maine, nine miles distant, whenever it was in operation.  He heard it best during a heavy northeast snow storm, the wind blowing then directly from him, and toward the source of the sound.  Gen. Duane also reported that “there are six fog-signals on the coast of Maine; these have frequently been heard at the distance of twenty miles,” ... which distance he gives as the extreme limit of the twelve-inch steam-whistle.