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Earth's Rotation

( Originally Published 1851 )

The earth which we inhabit is not precisely a spherical body, but a spheroid flattened at its poles, similar in shape to an orange. Its shortest diameter is about 7940 miles, its longest about 7966 miles ; their difference being about 26 miles.

This body passes through its orbit, which is nearly a circle of 190 millions of miles in diameter, in a solar year ; it also revolves uniformly upon its shorter diameter as an axis, so as to make a complete rotation in 23h. 56m. 4s. ; and that without the slightest variation, in all seasons of the year, and in all ages of the world. Laplace, from a comparison of numerous observations, ancient and modern, affirms that this is decidedly and unquestionably the most uniform motion which the universe presents to observation ; for, although the planetary rotations probably present the same positive uniformity, it is not accompanied with equally decisive evidence.

Now, to the same time of rotation, there are two widely different forms, each of which is equally consistent with stability. Thus, if the earth were a homogeneous body, the ratio of the polar to the equatorial axis might be either that of 1 to 680, or that of 229 to 130; the latter of these is the one which actually exists; its adoption is a proof of design, by which many inconveniences to the in-habitants are avoided, which, however, cannot now be detailed, without deviating from the immediate purpose of this article.

The earth is constituted partly of solid, partly of liquid matter, known under the general distinctions of land and water. If the solid matter had been formed into a precise here, and then the water created, that water, as soon as the earth received its rotation, would, by reason of the centrifugal force, have disposed itself about the equatorial regions, so as to cover them entirely with water. To prevent this, a protuberance has been given to the equatorial regions; and the forms, shapes, depths, contour, &c., of the land and water respectively, have been so mutually adjusted, not only there, but in every habitable part of the earth, as to promote, most exquisitely, the well-being of the inhabitants; so long as the period of rotation remains what it at first was. There could be but one time of rotation that would thus allow the waters just to fill certain cavities, and yet not to overflow the hills; that is, that would compel the general surface of the liquid parts to harmonize with that of the solid parts: and to produce that time of rotation about a given axis, a given force must act at a given point, and in a given direction. What but intelligence and design, operating fur a benevolent purpose, could cause the union of these three independent circumstances?

But farther, a more rapid rotation would cause more of the waters to flow towards the equatorial regions, and thus, if carried beyond a certain limit, to inundate the whole land there, and leave others dry; while a slower rotation would cause the waters to recede from the equatorial regions, and leave them dry, at the same time inundating the land in the temperate and other regions. So that the uniformity of rotation is essential to the well-being of the inhabitants of the earth; and yet there is a constant tendency to destroy that uniformity, which is as constantly prevented by the benevolent operation of' divine energy.

To understand the reason of this, let the following facts be considered. In consequence of the rotatory motion, night and day are always dividing between them the surface of the earth; and the day as incessantly rousing into activity that half of the inhabitants over whom the light of the sun is passing. Thus many millions of human beings are incessantly performing some mechanical action or other; and many thousand of animals, and many thousand of machines of different kinds, are as incessantly performing mechanical operations under their superintendence; and this with an inconceivable variety of effort, of direction, and of place, over the entire habitable surface of the globe. In all these actions, except those which are so regulated by refined knowledge and skill as to produce a maximum of effect with a given effort (not one in ten thousand probably,) there is a positive loss of mechanical power. WHAT BECOMES OF IT? Since action and reaction are equal and opposite, the amount of these losses of power is expended upon the earth, the necessary fulcrum of all our movements. Now, either all these milli ins of loses of power, incessantly occurring, must be directed towards the centre of the earth, which is infinitely improbable; or they must so occur, as every moment just to counterbalance and annihilate each other, which is also infinitely improbable; or they must constantly tend to change the velocity and duration of the earth's rotation, and thus to produce the evils which we have shown would result from such a change. It is, indeed, quite impossible to estimate the accumulation of mischief that would thus accrue, in one month, from ignorance in the application of human, animal, and mechanical agency; but a bare reference to the facts may serve to excite a train of devotional meditation upon " the goodness and mercy" that are constantly engaged in a wide field of providential operation which is thus laid open, and which is not the less real for being shut to the ken of our senses, since it is open to the enraptured view of intellect and science.

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