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.
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.
Pl. III. SEASONS.—Winter.