ifying climate, not so much by direct radiation
as by diffusion through the medium of the air.

This very obvious importance of aerial currents led to their practical
study long before meteorology had any title to the rank of science, and
Dalton's explanation of the trade-winds had laid the foundation for a
science of wind dynamics before the beginning of the nineteenth century.
But no substantial further advance in this direction was effected until
about 1827, when Heinrich W. Dove, of Konigsberg, afterwards to be known
as perhaps the foremost meteorologist of his generation, included
the winds among the subjects of his elaborate statistical studies in
climatology.

Dove classified the winds as permanent, periodical, and variable. His
great discovery was that all winds, of whatever character, and not
merely the permanent winds, come under the influence of the earth's
rotation in such a way as to be deflected from their course, and hence
to take on a gyratory motion--that, in short, all local winds are minor
eddies in the great polar-equatorial whirl, and tend to reproduce in
miniature the character of that vast maelstrom. For the first time,
then, temporary or variable winds were seen to lie within the province
of law.

A generation later, Professor William Ferrel, the American
meteorologist, who had been led to take up the subject by a perusal of
Maury's discourse on ocean winds, formulated a general mathematical law,
to the effect that any body moving in a right line along the surface of
the earth in any direction tends to have its course deflected, owing to
the earth's rotation, to the right hand in the northern and to the left
hand in the southern hemisphere. This law had indeed been stated as
early as 1835 by the French physicist Poisson, but no one then thought
of it as other than a mathematical curiosity; its true significance was
only understood after Professor Ferrel had independently rediscovered it
(just as Dalton rediscovered Hadley's forgotten law of the trade-winds)
and applied it to the motion of wind currents.

Then it became clear that here is a key to the phenomena of atmospheric
circulation, from the great polar-equatorial maelstrom which manifests
itself in the trade-winds to the most circumscribed riffle which is
announced as a local storm. And the more the phenomena were studied,
the more striking seemed the parallel between the greater maelstrom
and these lesser eddies. Just as the entire atm