tinct science and art. The germicidal
action of light-rays and of some of the invisible rays which ordinarily
accompany the luminous rays is well proved. Wounds are treated
effectively and water is sterilized by the ultraviolet radiant energy in
modern artificial illuminants.

Thousands of lighthouses, light-ships, and light-buoys are scattered
along sea-coasts, rivers, and channels. They guide the wheelman and warn
the lookout of shoals and reefs. Some of these send forth flashes of
light whose intensities are measured in millions of candle-power. Many
are unattended for days and even months. These powerful lights dominated
by automatic mechanisms have replaced the wood-fires which were
maintained a few centuries ago upon certain prominent points.

Signal-lights now guide the railroad train through the night. A burning
flare dropped from the rear of a train keeps the following train at a
safe distance. Huge search-lights penetrate the night air for many
miles. When these are equipped with shutters, a code may be flashed from
one ship to another or between the vessel and land. A code from a
powerful search-light has been read a hundred miles away because the
flashes were projected upon a layer of high clouds and were thus visible
far beyond the horizon.

Artificial light played its part in the recent war. Huge search-light
equipments were devised for portability. This mobile apparatus was
utilized against enemy aircraft and in various other ways. Small
hand-lamps are used to send out a pencil of light as directed by a pair
of sights and the code is flashed by means of a trigger. Raiding-parties
are no longer concealed by the curtain of darkness, for rockets and
star-shells are used to illuminate large areas. Flares sent upward to
drift slowly downward supported by parachutes saved and cost many lives
during the recent war. Rockets are used by ships in distress and also by
beleaguered troops.

Experiments are being prosecuted to ascertain the possibilities of
artificial light in the forcing of plant-growth, and even chickens are
made to work longer hours by its use.

Artificial light is now modified in color or spectral character to meet
many requirements. Daylight has been reproduced in spectral quality so
that certain processes requiring accurate discrimination of color are
now prosecuted twenty-four hours a day under artificial daylight.
Colored light is made of the correct quality which does not affect
photogra