CHAP. i. 20. INTRODUCTION. by no means constitute the majority of mankind, wl ally prefer that which holds out some direct advantage. The geographer should therefore chiefly devote himself to what is practically important. He should follow the same rule in regard to history and the mathematics, selecting always that which is most useful, most intelligible, and most au- thentic. 20. Geometry and astronomy, as we before remarked, seem absolutely indispensable in this science. This, in fact, is evi- dent, that without some such assistance, it would be impossi- ble to be accurately acquainted with the configuration of the earth ; its climat a, l dimensions, and the like information. As the size of the earth has been demonstrated by other writers, we shall here take for granted and receive as accurate what they have advanced. We shall also assume that the earth is spheroidal, that its surface is likewise""spheroidal, and above all, that bodies have a tendency towards its centre, which latter point is clear to the perception of the most aver- age understanding. However we may show summarily that the earth is spheroidal, from the consideration that all things however distant tend to its centre, and that every body is at- tracted towards its^ centre pToved from observations evidence of the senses, and common observation, is alone re- quisite. The convexity of the sea is a further proof of this to those who have sailed ; for they cannot perceive lights at a distance when placed at the same_level as tKeTr J^yes, but if raised on^high, they at once become perceptible to vision, tKough at the same time further removed. So, when the eye is raised, it sees what before was utterly imperceptible. Homer speaks of this when he says, Lifted up on the vast wave he quickly beheld afar. 2 Sailors, as they approach their destination, behold the shore continually raising itself to their view ; and objects which had at first seemed low, begin to elevate themselves. Our gnomons, also, are, among other things, evidence of the revolu- tiorfof the heavenly bodies ; and common seTTse at once shows us, 1 Vide preceding note on this word, p. 13, n. 1. 2 Odyssey v. 393. c 2 5 centre, and that every body is at- of Jjravity ; this is more distinctly of the sea and sky, for here the
