ceremonies.  Some of these have persisted to the present time.  The great pageants of peace celebrations and world’s expositions appropriately feature artificial light.  In drawing upon the potentiality of the expressiveness and impressiveness of light and color, artificial light is playing a major part.  Doubtless the future generations will be entertained by gorgeous symphonies of light.  Experiments are performed in this direction now and then, and it is reasonable to expect that after many centuries of cultivation of the appreciation of light-symphonies, these will take a place among the arts.  The elaborate and complicated music of the present time is appreciated by civilized nations only after many centuries of slow cultivation of taste and understanding.

Light-therapy is to-day a distinct 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.