Around the dry land of the earth are the oceans of water. We may never
have seen them, but we have knowledge of them and their navigation, and
their names suggest very definite and concrete objects of thought. We
sometimes do not realize, however, that we live and move and have our
being at the bottom of a vaster and deeper ocean that covers to a depth
of many miles the whole earth, and to the surface of which man nor beast
nor bird has ever ascended; an ocean with currents and whirlpools and
waves of more than mountain height; an ocean in which we are as much at
home as are the finny tribes and the monsters of the deep in their
watery caverns. This is the ocean of the air. We are about to consider
man's efforts to rise from the bottom of this ocean and wing his flight
a little way through the atmosphere above him. His excursions upward are
limited, for he could not live near the surface heights of this ocean,
vast and deep and boundless. The art and science of his flight through
the air, because of its relation to the flight of birds, we call
aviation. (_Avis_: Latin, a bird.)