THE SEASONS.
_Why their varying Temperature?_
The usual explanation of these phenomena, _i. e._, the influence of
direct and oblique sun-rays, has ever seemed insufficient and
unsatisfactory; especially in view of the _fact_ that the heat comes not
from the sun by continuity after the manner of progression as from a
heated body.
A philosophy more exact and consistent may be found in the development
of the theory already advanced, and which is illustrated in the
following plates.
_The maximum of heat at the surface of the earth bears a very constant
and intimate relation to the line of greatest diameters of the sun and
earth._--Pl. II. a.
Through this line the heat-producing functions of these great spheres
are in operation in the highest degree.
[Illustration: Pl. II. SEASONS.--SUMMER.]
This line of magnetic, or heat activity, consequently varies with the
earth's movements. On the 20th of June the flood of summer heat
overspreads the northern portions of the earth; the sun thence
apparently turns southward, and with its departure the relations of the
line of heat activity change. The city of New York, which on the 20th of
June is found nearest the centre of the solar current (Plate II. b), is,
on the 21st of December, located at its greatest distance from the line
of magnetic or heat intensity (Plate III. b), where the heat-producing
forces are in operation in but low degree.
[Illustration: Pl. III. SEASONS.--WINTER.]