The comparison of
observations made at places lying so many hundred miles apart, will decide,
for instance, whether the same east wind blows from the elevated desert of
Gobi to the interior of Russia, or whether the direction of the Aerial
current first began in the middle of the series of the stations, by the
descent of the air from the higher regions. By means of such observations,
we may learn, in the strictest sense, 'whence' the wind cometh. If we only
take the results on which we may depend from those places in which the
observations on the direction of the winds have been continued more than
twenty years, we shall find (from the most recent and careful calculations
of Wilhelm Mahlmann) that in the middle latitudes of the temperate zone, in
both continents, the prevailing aerial current has a west-southwest
direction.
Our insight into the 'distribution of heat' in the atmosphere has been
rendered more clear since the attempt has been made to connect together by
lines those places where the mean annual summer and winter temperatures have
been ascertain by correct observations. The system of 'isothermal,
osotheral' and 'isochimenal' lines, which I first brought into use in 1817,
may, perhaps, if it be gradually perfected by the united efforts of
investigators, serve as one of the main foundations of 'comparative
climatology'.
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