But the scientific editor in giving his needless information commits another blunder, which we could hardly expect from a man of science, by affirming that the Ptolemaic theory “was elucidated and confirmed by mathematics.” Mathematics confirmed nothing but the order and quality of the phenomena, and the law of their succession. Before Kepler and Newton no mathematics could decide whether the sun revolved around the earth or the earth around the sun. Astronomical phenomena were known, but this knowledge was a knowledge of facts, not of their explanation. The Ptolemaic hypothesis was not inconsistent with the facts then observed, but it was _assumed_, not _verified_. If such a theory had been verified, its truth would be still recognized, and the Copernican theory would have had no chance of admission. But evidently it is not the theory that has been verified, but only the apparent movements of celestial bodies. Thus “the elaborate tables” by which the future positions of the planets could be foretold prove indeed the accuracy of ancient astronomical observations and calculations, but they are no evidence that the geocentric theory was correct. Mr. Youmans informs us, also, that “Copernicus did not abolish, but rather revised, the old astronomy.” If the words “old astronomy” are taken to express merely the knowledge of celestial phenomena, we have nothing to reply; but if those words be understood to mean the Ptolemaic theory, the assertion is ridiculous. Indeed, Copernicus, as Mr. Youmans says, “simply recentred the solar system”; that is, he simply put the sun, instead of the earth, in the centre of the planetary orbits. Nothing but that. But who does not see that to give a new centre to the solar system was to suppress the old centre, and therefore to _abolish_ the geocentric theory? Why Mr. Youmans should labor to insinuate the contrary we cannot really understand. Dr. Taylor, against whom he writes, had said nothing concerning either the personal views of Copernicus or the old system of astronomy, but had simply maintained that the so-called Copernican theory, as mentioned by Prof. Huxley, and as understood by all—that is, as perfected by Kepler, Newton, and others—stands to-day on such a basis of undeniable facts that we can no longer hesitate about its truth. This statement might have been contradicted two centuries ago; but we fancy that it ought not to give rise to the least controversy on the part of a modern cultivator of science, however much determined to find fault with his opponent.