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.

Thus, artificial light has been an important factor in the great
industrial development of the present time. Man now burrows into the
earth, navigates under water, travels upon the surface of land and sea,
and soars among the clouds piloted by light of his own making. Progress
does not halt at sunset but continues twenty-four hours each day.
Building, printing, manufacturing, commerce, and other activities are
prosecuted continuously, the working-shifts changing at certain periods
regardless of the rising or setting sun. Adequate artificial lighting
decreases spoilage, increases production, and is a powerful factor in
the prevention of industrial accidents.

It has ever been true since the advent of artificial light that the
intellect has been largely nourished after the completion of the day's
work. The highly developed artificial lighting of the present time may
account for much of the vast industry of publication. Books, magazines,
and newspapers owe much to convenient and inexpensive artificial light,
for without it fewer hours would be available for recreation and
advancement through reading. Schools, libraries, and art museums may be
attended at night for the betterment of the human race. The immortal
Lincoln, it is said, gained his early education largely by the light of
the fireplace. But all were not endowed with the persistence of Lincoln,
so that illiteracy was more common in his day than in the present age of
adequate illumination.

The theatrical stage not only depends for its effectiveness upon