To this must be added what was said in the introduction, that the surprising accuracy of modern instruments and modern investigations, applied to meridian circles and parallels of latitude, have determined the fact that the spheroid is not a perfect one, (just as so often in nature the ideal is rather striven after than attained,) but an irregular polyhedron of an indeterminate number of sides. Still for all practical purposes, these minute inquiries have no value, and it is enough to treat of the earth as a perfect globe, so far, at least, as map-drawing is concerned. The deviation from a perfectly spherical shape is so inconsiderable that in an artificial globe of eighteen inches diameter it would hardly amount to the thickness of a sheet of paper; still, small as this is represented on a miniature scale, it has, doubtless, great importance on the great scale of a world like this, both in affecting somewhat the perturbation of other heavenly bodies which depend on the earth, as well as the perturbations in the earth’s own motion. Besides this, which is really not a small point in consideration of the possible results which the minutest perturbation of one little planet may have on the universe, there is one other, more appreciable in its results, the probable influence of this spheroidal, or rather polyhedrons form, in producing the unequal division of land and water upon the surface of the earth. The apparent want of any principle or reason for this inequality has long perplexed geographers, and there seems to be no more satisfactory solution than the one to which I have just alluded. In the course of future investigations into the yet undetermined exact mathematical form of the earth, the law which controls the division into land and water will be more thoroughly understood. Unquestionably the position of the great oceans depends upon their distance from the center of the globe, and although the present proportion of land and water seems fortuitous, undoubtedly it has a uniformly acting, and a thoroughly appreciable law. The Threefold Covering of the Earth.