of the knowledge of those remote periods.  Science as it exists to-day is founded upon proved facts.  The scientist, equipped with a knowledge of physical and chemical laws, is led by his imagination into the darkness of the unexplored unknown.  This knowledge illuminates the pathway so that hypotheses are intelligently formed.  These evolve into theories which are gradually altered to fit the accumulating facts, for along the battle area of progress there are innumerable scouting-parties gaining secrets from nature.  These are supported by individuals and by groups, who verify, amplify, and organize the facts, and they in turn are followed by inventors who apply them.  Liaison is maintained at all points, but the attack varies from time to time.  It may be intense at certain places and other sectors may be quiet for a time.  There are occasional reverses, but the whole line in general progresses.  Each year witnesses the acquirement of new territory.  It is seen that through the centuries there is an ever-growing momentum as knowledge, efficiency, and organization increase the strength of this invading army of scientists and inventors.

The burning fagot rescued mankind from the shackles of darkness, and the grease-lamp and tallow-candle have done their part.  Progress was slow in those early centuries because the great minds of those ages philosophized without a basis of established facts:  scientific progress resulted more from an accumulation of accidental discoveries than by a directed attack of philosophy supported by the facts established by experiment.  It was not until comparatively recent times, at most three centuries ago, that the great intellects turned to systematically organized scientific research.  Such men as Newton laid the foundation for the tremendous strides of to-day.  The store of facts increased and as the attitude changed from philosophizing to investigating, the organized knowledge grew apace.  All of this paved the way for the momentous successes of the present time.

The end is not in sight and perhaps never will be.  The unexplored region extends to infinity and, judged by the past, the momentum of discovery will continue to increase for ages to come, unless the human race decays through the comfort and ease gained from utilizing the magic secrets which are constantly being wrested from nature.  Among the achievements of science and invention, the production and application of artificial light ranks high.  As an influence upon civilization, no single achievement surpasses it.

Without artificial light, mankind would be comparatively inactive about one half its lifetime.  To-day it has been fairly well established that the human organism can flourish on eight hours’ sleep in a period of twenty-four hours.  Another eight hours spent in work should settle man’s obligation to the world.  The remaining hours should be his own.  Artificial light has made such a distribution of time possible.  The working-periods in many cases may be arranged in the interests of economy, which often means continuous operations.  The sun need not be considered when these operations are confined to interiors or localized outdoors.