The terrestrial globe being from that time recognized as isolated, to move it was no longer difficult. Formerly, when the sky was looked upon as a dome crowning the massive and unlimited Earth, the very idea of supposing it to be in motion would have been not only absurd but untenable. But from the time that we could see it in our minds, placed like a globe in the centre of celestial motion, the idea of imagining that perhaps this globe could revolve on itself, so as to avoid obliging the whole sky and the immense universe to perform this daily task, might come naturally into a thinker's mind; and indeed we see the hypothesis of the daily rotation of the terrestrial sphere coming to light in ancient civilizations, among the Greeks, the Egyptians, the Indians, etc. It is sufficient to read a few chapters of Ptolemy, Plutarch, or Surya-Siddhanta for an account of these conjectures. But this new hypothesis, although it had been prepared for by the first one, was none the less bold, and contrary to the feelings inspired by the direct contemplation of Nature. Thoughtful mankind was obliged to wait until the sixteenth century, or, to speak more correctly, until the seventeenth century, to learn our planet's true position in the universe, and to _know_ by supported proofs that it has a double movement,--daily about itself, and yearly about the Sun. From that time only, from the time of Copernicus, Galileo, Kepler, and Newton, has real astronomy existed. And yet again, that was but a beginning, for the great remodeller of the world's system, Copernicus himself, had no suspicion of the Earth's other motions, or of the distances of the stars. It is only in our own century that the first measurements of the distances of the stars could be made, and it is only in our day that sidereal discoveries have afforded us the necessary data by which we might endeavor to account for the forces which maintain the equilibrium of creation. The ancient idea of endless roots attributed to the Earth, evidently left much to be desired to minds anxious to go to the bottom of things. It is absolutely impossible for us to conceive of a material pillar, as thick and as wide as you like (of the diameter of the Earth, for example), sinking down into the infinite; just as one cannot admit the real existence of a stick which should have but one end. No matter how far our mind goes down towards the base of such a material pillar, there is a point where it can see the end of it. The difficulty had been obviated by materializing the celestial sphere and putting the Earth inside it, occupying all its lower portion. But in the first place it became difficult to adjust the motion of the stars, and on the other hand this material universe itself, enclosed in an immense crystal globe, was held up by nothing, since the infinite must extend all around, beneath it, as well as above. Investigating minds were at first obliged to free themselves from the vulgar idea of weight.