Hand Book of Physical Geography Author:Keith Johnston Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: LAND AND WATER. Map 2. The Earth has long been proved to have a globular form, by its having been circumnavigated, by the constantly circular shadow which it... more » throws on the moon during an eclipse, and by the phenomena of horizontal disappearance. Actual measurements of parts of the earth's surface show, however, that its form is not that of a perfect sphere, nor indeed of any mathematical body. To obtain the real length of the circumference of the earth, it was believed that by actually measuring by rule one degree of its surface, the length of it being marked out by the nadir points, or points vertically under two stars, a degree apart in the celestial sphere, and multiplying the degree thus measured by 360, the length of the circumference would be obtained; but most minute measurements of this kind, on various parts of the globe, show that the length of a degree varies in different parts of its surface, Form of the Earth, being longer towards the north pole and shorter towards the equator, thus pointing to a flattening of the globe at its poles, or a bulging out at the equatorial regions, giving the earth a spheroidal shape. The amount of this flattening, however, is different on the opposite sides of the globe, and the ratio of the difference between the polar and equatorial diameters of the earth, is found to vary between one 331st, and one 289th, part of the diameter, in favour of the equatorial axis. The form of the earth is, then, an irregular approach to a spheroid. The outer crust of this spheroid is also uneven, being hollowed out in the part of it which is covered by the sea, and raised in the parts which we call land,—the visible parts of the solid earth, which are above the level of the sea. Nearly three-fourths of the earth's solid crust is thus hid...« less