istances. 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 "th