g twilight. He
contemplates it as the prime mover in a variety of machines, as
impelling ships across the ocean, raising balloons to the region of the
clouds, blowing our furnaces, raising water from the deepest pits,
extinguishing fires, and performing a thousand other beneficent
agencies, without which our globe would cease to be habitable. No one
can doubt that all these views and contemplations have a direct tendency
to enlarge the capacity of the mind, to stimulate its faculties, and to
produce rational enjoyment.

But there is another view of this subject which is perhaps still more
impressive. The atmosphere, it has been stated, is a compound substance.
A knowledge of its elementary principles, which chemistry teaches,
introduces its possessor to a new world of happiness. The adaptation of
air to respiration, and the influence of a change in the nature or
proportion of its elements upon health and longevity, have already been
considered.[53] We have seen that carbonic acid, the vitiating product
of respiration, although immediately fatal to animals, constitutes the
very life of vegetation; that in the growth of plants the vitiated air
is purified and fitted again for the sustenance of animal life; and
that, by a beneficent provision of the Creator, animals and vegetables
are thus perpetually interchanging kindly offices. It will suffice for
our present purpose simply to remind the reader that the atmosphere is
composed of the two gases, oxygen and nitrogen, united in the ratio of
one to four by volume. Oxygen is a supporter of combustion, nitrogen is
not. Increase the proportion of oxygen in the air, and the same
substances burn with increased brilliancy; but diminish the proportion
gradually, and they will burn more and more dimly until they become
extinct. Iron and steel, as well as wood and the ordinary combustibles,
will burn with great brilliancy in pure oxygen.

[53] See Chapter IV., especially from the 89th page to the 105th.

Water, I may add, is composed of the two gases, oxygen and hydrogen. The
former, as we have seen, is a supporter of combustion, and the latter is
one of the most combustible substances known. These two gases are nearly
two thousand times more voluminous than their equivalent of water, and,
when ignited, they _combine with explosive energy_. If, then, the
Creator were to decompose the atmosphere that surrounds the earth to the
height of forty-five miles, and the water that res