UIHistories Project: A History of the University of Illinois by Kalev Leetaru
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Repository: UIHistories Project: Board of Trustees Minutes - 1871 [PAGE 151]

Caption: Board of Trustees Minutes - 1871
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143

maximum annual and diurnal heat, with its maximum focus of heat at its center, is the natural and necessary cause of the deflection of the trade-winds toward the west, and the upper return currents toward the east, so generally, however foolishly, attributed to the varying velocities of different parallels of latitude—as any one can see from a moment's reflection. For it is plain that the <cone or belt of maximum heat or wind-power on the earth's surface is not a single belt, encircling it from east to west near the equator, as is commonly represented, but a cross of belts, the one running east and west with its annual slides, the other at rignt angles to it, with its diurnal rotation and focus of maximum heat ever attending it. It may be, to some, an interesting coincidence, that our natural sun, at the maximum of his effulgence and power, exerts his paramount influence on our globe through a form of a cross, and not, as scientists have taught us, through one continuous mathematical line or belt around it. An adroit devotee to analogies, or correspondences, could write a whole ship-load of books on this simple fact, not wholly without interest. , II. When the sun is over the equator, and the days and nights are equal, the crepuscular line, as it has been called, or line of daylight, is parallel with the meridianal line of maximum heat, (A. B.); and the point or forces of greatest heat (O) will revolve on the equator. But when the days are longest, and the sun is over the tropic of Cancer, this line of daylight will be E. F.; which line will bound the hottest hemisphere of the globe, toward which all great air currents must tend E. A. C. F.; being deflected toward a line at right angles with the line E. F. This of course strengthens the tendency to our south and southwest winds in summer; for precisely the opposite reason, when in our shortest days in winter, the sun is over the tropic or calms of Capricorn, and this crepuscular line has swung around to 0. D., and C. F. B. D. becomes in turn the hottest hemisphere of the globe, all our winds tend more strongly to blow from the northwest toward the line C. D.—while our prevalent west winds, in March and September, are also measurably owing to this very obvious and simple course, as this line is then due north and south, or at A. B. These are the principal wellknown primal causes, which determine the perpetual flow and reflow of the great air-currents, and the peculiar climate of our globe. In a single word it is the power of the sun; and what a mighty power that is; and yet how gently, and quietly, and silently it works, through all its infinitely varied rounds and tasks! The means are as simple as the ends are various and infinite. Doubtless other local and modifying causes are as endless as they are varied; but here, alone, we find the great primal moving cause of all we behold in these incessant changes of seasons and years. DISCOURSE.

It will be my object, in this discourse, to give the present impressions which all my previous readings and reflections have made on my own mind, in regard to climate, without intending to cite at length the proofs of their correctness, nor indeed to affirm it at each and all points in question. Everybody knows that we are at present in no sort of condition to present a science of meteorology, and may not be for five hundred years to come; and the best way perhaps to help it along is for each one to state frankly his own impressions, a iree-will offering to the common stock. For the sake of brevity and directness, I shall, without intending to dogmatise, give my discourse wholly the dogmatic form, and let it pass