been more
than this, as will be shown later. During the same span of years the
percentage of carbon filament lamps of the total filament lamps sold
decreased from 100 per cent. in 1907 to 13 per cent. in 1917. At the
same time the percentage of tungsten (Mazda) lamps increased from
virtually zero in 1907 to about 87 per cent. in 1917. The tantalum lamp
had no opportunity to become established, because the tungsten lamp
followed its appearance very closely. In 1910 the sales of the former
reached their highest mark, which was only 3.5 per cent. of all the
lamps sold in the United States. From a lowly beginning the number of
incandescent filament lamps sold for use in this country has grown
rapidly, reaching nearly two hundred million in 1919.

XI

THE LIGHT OF THE FUTURE

In viewing the development of artificial light and its manifold effects
upon the activities of mankind, it is natural to look into the future.
Jules Verne possessed the advantage of being able to write into fiction
what his riotous imagination dictated, and so much of what he pictured
has come true that his success tempts one to do likewise in prophesying
the future of lighting. Surely a forecast based alone upon the past
achievements and the present indications will fall short of the actual
realizations of the future! If the imagination is permitted to view the
future without restrictions, many apparently far-fetched schemes may be
devised. It may be possible to turn to nature's supply of daylight and
to place some of it in storage for night use. One millionth part of
daylight released as desired at night would illuminate sufficiently all
of man's nocturnal activities. The fictionist need not heed the
scientist's inquiry as to how this daylight would be bottled. Instead of
giving time to such inquiries he would pass on to another scheme,
whereby earth would be belted with optical devices so that day could
never leave. When the sun was shining in China its light would be
gathered on a large scale and sent eastward and westward in these great
optical "pipe-lines" to the regions of darkness, thus banishing night
forever. The writer of fiction need not bother with a consideration of
the economic situation which would demand such efforts. This line of
conjecture is interesting, for it may suggest possibilities toward which
the present trend of artificial lighting does not point; however, the
author is constrained to treat the future of light-pro