6. Let it be supposed that this island is contained in one of the above quadrilaterals; we must obtain its apparent magnitude by subtracting our hemisphere from the whole extent of the earth, from this take the half, and from this again the quadrilateral, in which we state our earth to be situated. We may judge also by analogy of the figure of the whole earth, by supposing that it accords with those parts with which we are acquainted. Now as the portion of the northern hemisphere, between the equator and the parallel next the [north] pole, resembles a vertebre or joint of the back-bone in shape, and as the circle which passes through the pole divides at the same time the hemisphere and the vertebre into two halves, thus forming the quadrilateral; it is clear that this quadrilateral to which the Atlantic is adjacent, is but the half of the vertebre; while at the same time the inhabited earth, which is an island in this, and shaped like a chlamys or soldier’s cloak, occupies less than the half of the quadrilateral. This is evident from geometry, also[710] from the extent of the surrounding sea, which covers the extremities of the continents on either side, compressing them into a smaller figure, and thirdly, by the greatest length and breadth [of the earth itself]. The length being 70,000 stadia, enclosed almost entirely by a sea, impossible to navigate owing to its wildness and vast extent, and the breadth 30,000 stadia, bounded by regions rendered uninhabitable on account either of their intense heat or cold. That portion of the quadrilateral which is unfitted for habitation on account of the heat, contains in breadth 8800 stadia, and in its greatest length 126,000 stadia, which is equal to one half of the equator, and larger than one half the inhabited earth; and what is left is still more. 7. These calculations are nearly synonymous with those furnished by Hipparchus, who tells us, that supposing the size of the globe as stated by Eratosthenes to be correct, we can then subtract from it the extent of the inhabited earth, since in noting the celestial appearances [as they are seen] in different countries, it is not of much importance whether we make use of this measure, or that furnished by later writers. Now as the whole circle of the equator according to Eratosthenes contains 252,000 stadia, the quarter of this would be 63,000, that is, the space from the equator to the pole contains fifteen of the sixty divisions[711] into which the equator itself is divided. There are four [divisions] between the equator and the summer tropic or parallel passing through Syene. The distances for each locality are calculated by the astronomical observations.