n, with a little Carbonic Acid,
Aqueous Vapor, and a trace of Carburetted Hydrogen. There are
numerous well-known calculations of the proportions of the various
constituents of the atmosphere, which we owe to Priestley, Dalton,
Black, Cavendish, Liebig, and others; but that given by Professor
Ansted is sufficiently simple and intelligible. In 10 volumes or
parts of it, he gives to

Oxygen, the great supporter of life 2.100
Nitrogen, (not condensible under 50
atmospheres, and not respirable or
combustible,) 7.750
Aqueous Vapor .l42
Carbonic Acid .004
Carburetted Hydrogen .004
______
10.000

and he adds a trace of Ammoniacal Vapor. It is _usual_ to state the
proportions of air as being 1 Oxygen to 4 Nitrogen.

It is a curious fact, that, while there are six varieties of compounds
of nitrogen and oxygen, but one of these is fitted to sustain life,
and that is our atmosphere.

It is well enough to note, that, when we use the word volume or
measure, in speaking of the atmosphere or any gaseous body, we adopt
the theory of Gay-Lussac, who discovered that gases unite with each
other in definite proportions whenever they enter into combination.
This theory led to important results; for by knowing the elements of a
compound gas, we easily determine its specific gravity.

It has been attempted to apply the principle to organic bodies;
but it has not yet been carried to a full and satisfactory
conclusion. It may be noticed, too, that Dalton affirmed that
simple substances unite with each other in definite weights
to form compound substances, thus supporting the idea of
Lussac. These discoveries were made about the same time,
Dalton having the credit of originating them. Various modifications
of the principle have been from time to time presented to public
attention.

Whether the constituents of the atmosphere are chemically or
mechanically combined,--one of the things about which the learned are
not fully agreed,--it is found to be chemically the same in its
constituents, all over the world, whether collected on mountains or on
plains, on the sea or on the land, whether obtained by aeronauts miles
above the earth or by miners in their deepest excavations. On the
theory of its mechanical combination, however, as by volume, and that
each constitue