contradictory in its character—Philosophy of the barometric change—No aid to be derived from these theories

232   CHAPTER X. Further inquiry in relation to the reciprocal action between the earth and the counter-trade—Terrestrial magnetism, and what we know of it—Its elements, and their variations—Their connection with the variations of atmospheric condition—Magnetism acts through its connection with electricity—Character of the latter and its variations—Their connection with atmospheric conditions—Electricity as well as magnetism in excess over this country—Effects of it upon our climate—Closer consideration of the atmospheric phenomena—Their diurnal changes and connections compared with those of magnetism and electricity—Grouping of all the diurnal variations—Particular and separate examination of them—Classification of storms—Examination in detail of the several classes and the primary influence of the earth or counter-trade in relation to each 285   CHAPTER XI. Prognostics 340

 

 

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THE PHILOSOPHY OF THE WEATHER.

 

CHAPTER I.

Heat and moisture are indispensable to the fertility of the earth. Without suitable arrangements for their diffusion and distribution, and within the limits of certain minima and maxima, it would not have been habitable, or the design of its Creator perfected. These arrangements therefore exist, and “while the earth remaineth seed time and harvest shall not cease.” Few and simple in their character, though necessarily somewhat complicated and irregular in their operation, the ultimate result is always attained. A beautiful system of compensations supplies the losses of every apparent irregularity in one section or crop, by the abundance of others.

From the operation of these few, simple, connected, and intelligible arrangements for the diffusion of heat and the distribution of moisture over the earth, result all the phenomena which constitute the weather; and by studying them, and their operation, we may acquire an accurate knowledge of its “Philosophy.”

The necessary heat is furnished, or produced, mainly by the direct action of the sun’s rays; and the most obvious feature in the arrangements for its diffusion is that by which the sun is made to shine successively and alternately upon different portions of the earth. Nothing animate or organic could endure his burning rays, if they shone continuously or vertically upon one point, or could exist without their occasional presence. Hence the provision for a diurnal rotation, to prevent the exposure of any portion of the globe to the action of those rays for twenty-four consecutive hours, except for a limited period, and at a considerable angle, in the polar regions. But the earth is spheroidal, and a diurnal revolution would still leave that portion which lies under the equator too much, and the other too little, exposed to the action of the sun. This is obviated by an annual revolution of the earth around the sun, and an obliquity of its axis, by reason of which the northern and southern portions are alternately and, as far as the tropics vertically, exposed to the sun; and it is made to travel (so to speak) from tropic to tropic, producing summer and winter, and other important phenomena.

This obliquity and consequent change of exposure are in degree precisely what the wants of the earth would seem to require. If it was greater, the sun would travel further north and south, but the alternate winters would be longer and more severe. If it was less, the end would not be as perfectly attained.

The direct action of the sun’s rays upon the earth, particularly those portions which lie north and south of the tropics, is not the only source from which the supply of heat is derived. Although there is a general increase of heat in spring and summer when the sun travels north, and of cold when he travels south in winter, yet there are frequent irregularities attending both. Very sudden and great changes occur in each of them. Frost sometimes, cool weather often, occurs in midsummer, and considerable heat and tornadoes in midwinter. And ordinarily the maxima and minima of each month and, indeed, of each week are widely apart. Even in the polar regions, in midwinter, where the sun does not shine at all, the same moderating changes with which we are conversant occur in degree. An extract or two from the register found in Dr. Kane’s narrative of the “Grinnell Expedition” will illustrate this.

January 1851, (Latitude about 74°, Longitude about 70°).

Date.	Wind.	Force.	Ther.	Bar.	Sky and Weather.
Jan. 3	......	calm	-26.1	29.62	blue sky, m.
"4	W.	gent breeze	-21.3	29.53	blue sky, detached clouds, m.
"5	W. by N.	gent breeze	-3.9	29.59	blue sky, m., clouded over.
"6	W. by S.	light breeze	-0.8	29.67	clouded over, m., snow.
"7	W.	gent breeze	-14.4	29.96	blue sky, detached clouds, m.
"8	W.S.W.	light air	-21.2	30.14	blue sky, m.
"29	W.N.W.	light air	-18.9	30.19	blue sky.
"30	NW. by W.	light air	-13.5	30.17	clouded over, m.