3. The heavens and the earth must be supposed to be divided each into five zones, and the celestial zones to possess the same names as those below. The motives for such a division into zones we have already detailed. These zones may be distinguished by circles drawn parallel to the equator, on either side of it. Two of these will separate the torrid from the temperate zones, and the remaining two, the temperate from the frigid. To each celestial circle there shall be one corresponding on earth, and bearing the same name, and likewise zone for zone. The [two] zones capable of being inhabited, are styled temperate. The remaining [three] are uninhabitable, one on account of the heat, the others because of the extreme cold. The same is the case with regard to the tropical, and also to the arctic circles, in respect of those countries for which arctic circles can be said to exist. Circles on the earth are supposed, corresponding to those in the heavens, and bearing the same name, one for one.
As the whole heaven is separated into two parts by its equator, it follows that the earth must, by its equator, be similarly divided. The two hemispheres, both celestial and terrestrial, are distinguished into north and south. Likewise the torrid zone, which is divided into two halves by the equator, is distinguished as having a northern and southern side. Hence it is evident that of the two temperate zones, one should be called northern, the other southern, according to the hemisphere to which it belongs. The northern hemisphere is that containing the temperate zone, in which looking from east to west, you will have the pole on your right hand, and the equator on the left, or, in which, looking south, the west will be on the right hand, and the east on the left. The southern hemisphere is exactly the contrary to this.
It is clear that we are in one or other of these hemispheres, namely, the north; we cannot be in both:
“Broad rivers roll, and awful floods between,
But chief the ocean.”707
And next is the torrid zone. But neither is there any ocean in the midst of the earth wherein we dwell, dividing the whole thereof, nor yet have we any torrid region. Nor is there any portion of it to be found in which the climata are opposite to those which have been described as characterizing the northern temperate zone.
4. Assuming these data, and availing himself likewise of astronomical observations, by which the position of every place is properly determined, whether with respect to the circles parallel to the equator, or to those which cut these latter at right angles, in the direction of the poles, the geometer measures the region in which he dwells, and [judges of the extent of] others by comparing the distance [between the corresponding celestial signs]. By this means he discovers the distance from the equator to the pole, which is a quarter of the largest circle of the earth; having obtained this, he has only to multiply by four, the result is the [measure of the] perimeter of the globe.
In the same manner as he who takes the measures of the earth, borrows the foundation of his calculations from the astronomer, who himself is indebted to the natural philosopher, so in like manner the geographer adopts certain facts laid down as established by the geometer, before setting forth his description of the earth we inhabit; its size, form, nature, and the proportion it bears to the whole earth. These latter points are the peculiar business of the geographer. He will next enter on a particular description of every thing deserving notice, whether on land or sea; he will likewise point out whatever has been improperly stated by those who have preceded him, especially by those who are regarded as chief authorities in these matters.708
5. Let it be supposed that the earth and sea together form a spheroidal body, and preserve one and the same level in all the seas. For though some portions of the earth may be higher, yet this bears so small a relation to the size of the whole mass, as need not be noticed. The spheroid in consequence is not so minutely exact as one might be made by the aid of a turner’s instrument, or as would answer the definition of a geometer, still in general appearance, and looked at roughly, it is a spheroid. Let the earth be supposed to consist of five zones, with (1.) the equatorial circle described round it, (2.) another parallel to this,709 and defining the frigid zone of the northern hemisphere, and (3.) a circle passing through the poles, and cutting the two preceding circles at right angles. The northern hemisphere contains two quarters of the earth, which are bounded by the equator and the circle passing through the poles.
Each of these [quarters] should be supposed to contain a four-sided district, its northern side being composed of one half of the parallel next the pole; its southern, by the half of the equator; and its remaining sides, by [two] segments of the circle drawn through the poles, opposite to each other, and equal in length. In one of these quadrilaterals (which of them is of no consequence) the earth that we inhabit is situated, surrounded by sea, and similar to an island. This, as we said before, is evident both to our senses and to our reason. But should any one doubt thereof, it makes no difference so far as Geography is concerned, whether you suppose the portion of the earth we inhabit to be an island, or only admit what we know from experience, viz. that whether you start from the east or west, you may sail all round it. Certain intermediate spaces may have been left [unexplored], but these are as likely to be occupied by sea, as uninhabited lands. The object of the geographer is to describe known countries; those which are unknown he passes over equally with those beyond the limits of the inhabited earth. It will therefore be sufficient for describing the contour of the island we have been speaking of, if we join by a right line the utmost points which, up to this time, have been explored by voyagers along the coast on either side.
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, also710 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 divisions711 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