Geometry and astronomy, as we before remarked, seem absolutely indispensable in this science. This, in fact, is evident, that without some such assistance, it would be impossible to be accurately acquainted with the configuration of the earth; its climata,1 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 average 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 attracted towards its centre of gravity; this is more distinctly proved from observations of the sea and sky, for here the evidence of the senses, and common observation, is alone requisite. 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 their eyes, but if raised on high, they at once become perceptible to vision, though 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,
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 revolution of the heavenly bodies; and common sense at once shows us, that if the depth of the earth were infinite,3 such a revolution could not take place. Every information respecting the climata4 is contained in the ‘Treatises on Positions.’5
“ Lifted up on the vast wave he quickly beheld afar.2”Odyssey v. 393.