100 years is about the tenure of our coal fields, according to the
present rate of increase in the consumption. Whichever view we take,
sooner or later the end must ultimately come when the coal will be
exhausted; when the great mainspring of our commercial enterprise will
be gone, and we shall revert to that condition in which we were before
the coal fields were worked. In this point of view, therefore, coal has
an especial interest to us as engineers. If coal is important in this
direction, it is no less important in a purely scientific point of view,
apart from any mercantile end.

The chemist or physicist will tell you the wondrous story that the black
substance which you burn is simply so much light and heat and motion
borrowed from the sun and invested in the tissues of plants. He will
tell you that when you sit round your firesides the flame which enlivens
you, and the gas which enables you to read, and which civilizes you, is
nothing in the world but so much sunlight and so much sunheat bottled up
in the tissues of vegetables, and simply reproduced in your grates and
gas burners. Very few persons, I am afraid, realize this, which is one
of the many stories which science in its higher teachings shows us--one
of those fairy tales which are the result of the most careful scientific
investigation. Of the hundred and odd million tons of coal which we in
this country burn in the course of a year, about 20,000,000 tons are
thrown on our house fires; 30,000,000 tons find their way into our blast
furnaces, or are otherwise used in the smelting and manufacture of
metals; about 48,000,000 are burnt under steam boilers; 6,000,000 are
used in gas-making; while the remainder is consumed in potteries, glass
works, brick and lime kilns, chemical works, and other sundries which I
need not speak of.

To go into the chemistry of coal is quite sufficient to take up more