estigation was the conclusion
that for ordinary lighthouse purposes the oil-and gas-lamps were more
suitable and economical than arc-lamps; but where great range was
desired, the latter were much more advantageous, owing to their great
luminous intensity. Electric incandescent filament lamps have been used
for the less important lights, and recently there has been some
application of the modern high-efficiency filament lamps.

Besides the high towers there are many minor beacons, light-ships, and
light-buoys in use. Many of these are untended and therefore must
operate automatically. The light-ship is used where it is impracticable
or too expensive to build a lighthouse. Inasmuch as it is anchored in
fairly deep water, it is safe in foggy weather to steer almost directly
toward its position as indicated by the fog-signal. Light-ships are more
expensive to maintain than lighthouses, but they have the advantages of
smaller cost and of mobility; for sometimes it may be desired to move
them. The first light-ship was established in 1732 near the mouth of the
Thames, and the first in this country was anchored in Chesapeake Bay
near Norfolk in 1820. The early ships had no mode of self-propulsion,
but the modern ones are being provided with their own power. Oil and gas
have been used as fuel for the light-sources and in 1892 the U. S.
Lighthouse Board constructed a light-ship with a powerful electric
light. Since that time several have been equipped with electric lights
supplied by electric generators and batteries.

Untended lights were not developed until about 1880, when Pintsch
introduced his welded buoys filled with compressed gas and thereby
provided a complete lighting-plant. With improvements in lamps and
controls the untended light-buoys became a success. The lights burn for
several months, and even for a year continuously; and the oil-gas used
appears to be very satisfactory. Recently some experiments have been
made with devices which would be actuated by sunlight in such a manner
that the light would be extinguished during the day excepting a small
pilot-flame. By this means a longer period of burning without attention
may be obtained. Electric filament lamps supplied by batteries or by
cables from the shore have been used, but the oil-gas buoy still remains
in favor. Acetylene has been employed as a fuel for light-buoys.
Automatic generators have been devised, but the high-pressure system is
more simple. In the lat