.

Smaller signal-lamps using acetylene have been employed in the forestry
service and in other activities where a portable device is necessary. In
one type, a mixture-tank containing calcium carbide and water is of
sufficient capacity for three hours of signaling. A small pilot-light is
permitted to burn constantly and the flashes are obtained by operating a
key which increases the gas-pressure. The light flares as long as the
key is depressed. The range of this apparatus is from ten to twenty
miles. An electric lamp supplied from a storage battery has been
designed for geodetic operations in mountainous districts where it is
desired to send signals as far as one hundred miles. Tests show that
this device is a hundred and fifty times more powerful than the ordinary
acetylene signal-lamp, and it is thought that with this new electric
lamp haze and smoke will seldom prevent observations.

Certain fixed lights are required by law on a vessel at night. When it
is under way there must be a white light at the masthead, a starboard
green light, a port red light, a white range-light, and a white light at
the stern. The masthead light is designed to emit light through a
horizontal arc of twenty points of the compass, ten on each side of dead
ahead. This light must be visible at a distance of five miles. The port
and starboard lights operate through a horizontal arc of twenty points
of the compass, the middle of which is dead ahead. They are screened so
as not to be visible across the bow and they must be intense enough to
be visible two miles ahead. The masthead light is carried on the
foremast and the range-light on the mainmast, at an elevation fifteen
feet higher than the former. The range-light emits light toward all
points of the compass and must be intense enough to be seen at a
distance of three miles. The stern light is similar to the masthead, but
its light must not be visible forward of the beam. When a vessel is
towing another it must display two or three lights in a vertical line
with the masthead light and similar to it. The lights are spaced about
six feet apart, and two extra ones indicate a short tow and three a long
one. A vessel over a hundred and fifty feet long when at anchor is
required to display a white light forward and aft, each visible around
the entire horizon. These and many other specifications indicate how
artificial light informs the mariner and makes for order in shipping.
Without artificial lig