It might appear at first sight that it was carrying things too far to attribute to the Druids the knowledge, not indeed of the true system of the world, but the general idea on which it was constructed. But, on closer examination, this opinion seems to have some consistency. If it was from the Druids that Pythagoras derived the basis of his theology, why should it not be from them that he derived also that of his astronomy? Why, if there is no difficulty in seeing that the principle of the subordination of the earth might arise from the meditations of an isolated spirit, should there be any more difficulty in thinking that the principles of astronomy should take birth in the midst of a corporation of theologians embued with the same ideas as the philosophers on the circulation of life, and applied with continued diligence to the study of celestial phenomena. The Druid, not having to receive mythological errors, might be led by that circumstance to imagine in space other worlds similar to our own. Independently of its intrinsic value, this supposition rests also upon the testimony of historians. A singular statement made by Hecataeus with regard to the religious rites of Great Britain exhibits this in a striking manner. This historian relates that the moon, seen in this island, appears much larger than it does anywhere else, and that it is possible to distinguish mountains on its surface, such as there are on the earth. Now, how had the Druids made an observation of this kind? It is of not much consequence whether they had actually seen the lunar mountains or had only imagined them, the curious thing is that they were persuaded that that body was like the earth, and had mountains and other features similar to our own. Plutarch, in his treatise _De facie in orbe Lunae_, tells us that, according to the Druids, and conformably to an idea which had long been held in science, the surface of the moon is furrowed with several Mediterraneans, which the Grecian philosophers compare to the Red and Caspian seas. It was also thought that immense abysses were seen, which were supposed to be in communication with the hemisphere that is turned away from the earth. Lastly, the dimensions of this sky-borne country were estimated; (ideas very different to those that were current in Greece): its size and its breadth, says the traveller depicted by the writer, are not at all such as the geometers say, but much larger.