In Phaedo, Socrates speculates about the heavens, and develops an imaginative hypothesis that shows both the power and limits of reasoning by analogy from one data point:
This is what I believe, then, said Socrates. In the first place, if the earth is spherical and in the middle of the heavens, it needs neither air nor any other such force to keep it from falling; the uniformity of the heavens and the equilibrium of the earth itself are sufficient to support it. Any body in equilibrium, if it is set in the middle of a uniform medium, will have no tendency to sink or rise in any direction more than another, and having equal impulses will remain suspended. This is the first article of my belief.
I believe that it is vast in size, and that we who dwell between the river Phasis and the Pillars of Hercules inhabit only a minute portion of it—we live round the sea like ants or frogs round a pond—and there are many other peoples inhabiting similar regions. There are many hollow places all round the earth, places of every shape and size, into which the water and mist and air have collected. But the earth itself is as pure as the starry heaven in which it lies, and which is called aether by most of our authorities. The water, mist, and air are the dregs of this aether, and they are continually draining into the hollow places in the earth. We do not realize that we are living in its hollows, but assume that we are living on the earth’s surface. Imagine someone living in the depths of the sea. He might think that he was living on the surface, and seeing the sun an the other heavenly bodies through the water; he might think that the sea was the sky. He might be so sluggish and feeble that he had never reached the top of the sea, never emerged and raised his head from the sea into this world of ours, and seen for himself—or even heard from someone who had seen it—how much purer and more beautiful it really is than the one in which his people lives. Now we are in just the same position. Although we live in a hollow of the earth, we assume that we are living on the surface, and we call the air heaven, as though it were the heaven through which the stars move. And this point too is the same, that we are too feeble and sluggish to make our way out to the upper limit of the air. If someone could reach to the summit, or put on wings and fly aloft, when he put up his head he would see the world above, just as fishes see our world when they put up their heads out of the sea. And if his nature were able to bear the sight, he would recognize that it is the true heaven and the true light and the true earth. For this earth and its stones and all the regions in which we live are marred and corroded, just as in the sea everything is corroded by the briine, an there is no vegetation worth mentioning, and scarcely any degree of perfect formation, but only caverns and sand and measureless mud, and tracts of slime wherever there is earth as well, and nothing is in the least worthy to be judged beautiful by our standards. But the things above excel those of our world to a degree far greater still.
The real earth, viewed from above, is supposed to look like one of these balls made of twelve pieces of skin, variegated and marked out in different colors, of which the colors which we know are only limited samples, like the paints which artists use, but there the whole earth is made up of such colors, and others far brighter and purer still. One section is marvelously beautiful purple, and another is golden. All that is white of it is whiter than chalk or snow, and the rest is similarly made up of the other colors, still more and lovelier than those which we have seen. Even these very hollows in the earth, full of water and air, assume a kind of color as they gleam amid the different hues around them, so that there appears to be one continuous surface of varied colors. […] There are many kinds of animals upon it, and also human beings, some of whom live inland, others round the air, as we live round the sea, and others in islands surounded by air but close to the mainland. In a word, as water and the sea are to us for our purposes, so is air to them, and as air is to us, so the aether is to them.