Astronomical Myths: Based on Flammarions's "History of the Heavens"

by J. F. Blake; Camille Flammarion

One of the greatest writers on ancient geography was Strabo, whose ideas we will now give an account of. He seems to have been a disciple of Hipparchus in astronomy, though he criticises and contradicts him several times in his geography. He had a just idea of the sphericity of the earth; but considered it as the centre of the universe, and immovable. He takes pains to prove that there is only one inhabited earth—not in this refuting the notion that the moon and stars might have inhabitants, for these he considered to be insignificant meteors nourished by the exhalations of the ocean; but he fought against the fact of there being on this globe any other inhabited part than that known to the ancients.

It is remarkable to notice that the proofs then used by geographers of the sphericity of the earth are just those which we should use now. Thus Strabo says, "The indirect proof is drawn from the centripetal force in general, and the tendency that all bodies have in particular towards a centre of gravity. The direct proof results from the phenomena observed on the sea and in the sky. It is evident, for example, that it is the curvature of the earth that alone prevents the sailor from seeing at a distance the lights that are placed at the ordinary height of the eye, and which must be placed a little higher to become visible even at a greater distance; in the same way, if the eye is a little raised it will see things which previously were hidden." Homer had already made the same remark.

On this globe, representing the world, Strabo and the cosmographers of his time placed the habitable world in a surface which he describes in the following way: "Suppose a great circle, perpendicular to the equator, and passing through the poles to be described about the sphere. It is plain that the surface will be divided by this circle, and by the equator into four equal parts. The northern and southern hemispheres contain, each of them, two of these parts. Now on any one of these quarters of the sphere let us trace a quadrilateral which shall have for its southern boundary the half of the equator, for northern boundary a circle marking the commencement of polar cold, and for the other sides two equal and opposite segments of the circle that passes through the poles. It is on one such quadrilateral that the habitable world is placed." He figures it as an island, because it is surrounded on all sides by the sea. It is plain that Strabo had a good idea of the nature of gravity, because he does not distinguish in any way an upper or a lower hemisphere, and declares that the quadrilateral on which the habitable world is situated may be any one of the four formed in this way.

The form of the habitable world is that of a "chlamys," or cloak. This follows, he says, both from geometry and the great spread of the sea, which, enveloping the land, covers it both to the east and to the west and reduces it to a shortened and truncated form of such a figure that its greatest breadth preserved has only a third of its length. As to the actual length and breadth, he says, "it measures seventy thousand stadia in length, and is bounded by a sea whose immensity and solitude renders it impassable; while the breadth is less than thirty thousand stadia, and has for boundaries the double region where the excess of heat on one side and the excess of cold on the other render it uninhabitable."

The habitable world was thus much longer from east to west than it was broad from north to south; from whence come our terms longitude, whose degrees are counted in the former direction, and latitude, reckoned in the latter direction.

Eratosthenes, and after him Hipparchus, while he gives larger numbers than the preceding for the dimensions of the inhabited part of the earth, namely, thirty-eight thousand stadia of breadth and eighty thousand of length, declares that physical laws accord with calculations to prove that the length of the habitable earth must be taken from the rising to the setting of the sun. This length extends from the extremity of India to that of Iberia, and the breadth from the parallel of Ethiopia to that of Ierne.

That the earth is an island, Strabo considers to be proved by the testimony of our senses. For wherever men have reached to the extremities of the earth they have found the sea, and for regions where this has not been verified it is established by reasoning. Those who have retraced their steps have not done so because their passage was barred by any continent, but because their supplies have run short, and they were afraid of the solitude; the water always ran freely in front of them.

It is extraordinary that Strabo and the astronomers of that age, who recognised so clearly the sphericity of the earth and the real insignificance of mountains, should yet have supposed the stars to have played so humble a part, but so it was; and we find Strabo arguing in what we may call quite the contrary direction. He says, "the larger the mass of water that is spread round the earth, so much more easy is it to conceive how the vapours arising from it are sufficient to nourish the heavenly bodies."

Fig. 33.—The Earth of the Later Greeks.