which the fishes live, and it is a liquid which our eyes can
perceive.

But let us suppose for a moment that a being, whose eyes were so
made that he could see gases as we see liquids, was looking down
from a distance upon our earth. He would see an ocean of air, or
aerial ocean, all round the globe, with birds floating about in
it, and people walking along the bottom, just as we see fish
gliding along the bottom of a river. It is true, he would never
see even the birds come near to the surface, for the highest-
flying bird, the condor, never soars more than five miles from
the ground, and our atmosphere, as we shall see, is at least 100
miles high. So he would call us all deep-air creatures, just as
we talk of deep-sea animals; and if we can imagine that he fished
in this air-ocean, and could pull one of us out of it into space,
he would find that we should gasp and die just as fishes do when
pulled out of the water.

He would also observe very curious things going on in our air-
ocean; he would see large streams and currents of air, which we
call winds, and which would appear to him as ocean-currents do to
us, while near down to the earth he would see thick mists forming
and then disappearing again, and these would be our clouds. From
them he would see rain, hail and snow falling to the earth, and
from time to time bright flashes would shoot across the air-
ocean, which would be our lightning. Nay even the brilliant
rainbow, the northern aurora borealis, and the falling stars,
which seem to us so high up in space, would be seen by him near
to our earth, and all within the aerial ocean.