but little in United States waters. The term "effective range" is used
here to signify the actual distance at which, under the most unfavorable
circumstances, a signal can generally be heard on board of a paddle-wheel
steamer in a heavy sea-way.

_Guns._--The use of guns is not so great as it once was. Instances are on
record in which they were quite serviceable. Admiral Sir A. Milne said he
had often gone into Halifax harbor, in a dense fog like a wall, by the
sound of the Sambro fog gun. But in the experiments made by the Trinity
House off Dungeness in January, 1864, in calm weather, the report of an
eighteen-pounder, with three pounds of powder, was faint at four miles.
Still, in the Trinity House experiments of 1865, made in light weather
with a light gun, the report was clearly heard seven miles away. Dr.
Gladstone records great variability in the range of gun-sound in the
Holyhead experiments. Prof. Henry says that a twenty-four-pounder was used
at Point Boneta, San Francisco Bay, Cal., in 1856-57, and that, by the
help of it alone, vessels came into the harbor during the fog at night as
well as in the day, which otherwise could not have entered. The gun was
fired every half hour, night and day, during foggy and thick weather in
the first year, except for a time when powder was lacking. During the
second year there were 1,582 discharges. It was finally superseded by a
bell-boat, which in its turn was after a time replaced by a siren. A gun
was also used at West Quoddy Head, Maine. It was a carronade, five feet
long, with a bore of five and one-quarter inches, charged with four pounds
of powder. The gun was fired on foggy days when the Boston steamer was
approaching the lighthouse from St. Johns, and the firing was begun when
the steamer's whistle was heard, often when she was six miles away, and
was kept up as fast as the gun could be loaded, until the steamer answered
with its whistle.