“When a man undertakes to state the evidence of a theory, and gives us proofs that equally sustain an opposite theory, we naturally conclude that he does not know what he is talking about. This is very much Dr. Taylor’s predicament. In trying to contrast the evidence for evolution with the demonstrative proofs of the Copernican theory, he cites facts that are not only as good, but far better, to prove the truth of its antagonist, the Ptolemaic theory.”
Our readers will probably ask how it is possible to prove that a thing is black by the very facts which prove, even better, that the thing is white? That certain facts may be insufficient to prove either the one or the other of two opposite theories every one will admit; but that facts which are good to prove the movement of the earth are even better to prove its immobility, is what Mr. Youmans alone has the privilege of understanding.
Dr. Taylor, in his argument against Prof. Huxley, assumed the truth of the modern astronomical theory, and said that this theory was proved by facts presently occurring before our eyes; which is not the case with the hypothesis of evolution. But, as he did not mention in particular those facts which are considered to constitute the most irrefragable proof of the theory, his silence about them is interpreted by Mr. Youmans as an effect of ignorance. It is not our affair to defend Dr. Taylor; but we think that this interpretation is unfair. The reverend doctor was not writing a treatise of astronomy; he was simply stating a known doctrine, of which it was not his duty to make the demonstration. On the other hand, even if we admitted that the reverend doctor knows but little of astronomy, we do not see that this would weaken his argument; for, whether he knows much or nothing in this branch of science, it remains true that the Copernican theory is proved “by facts presently occurring before our eyes”—which is not the case with the hypothesis of evolution. It is to this truth that Mr. Youmans should have given his attention, if he desired “to win any distinction in the field of logic”; but his peculiar logic shrank from this duty, and prompted him to prefer a gratuitous denunciation of his opponent.
Mr. Youmans pretends that Dr. Taylor “talks as if the Copernican theory is something that anybody can see by looking up in the sky.” Dr. Taylor’s words do not admit of such a nonsensical construction. The Copernican theory, he says, “rests on facts presently occurring before our eyes, and treated in the manner of mathematical precision.” This obviously means that the Copernican theory is based on both observation and calculation. Now, surely Mr. Youmans will not maintain that we can find mathematical formulas and make astronomical calculations by simply “looking up in the sky.”
He goes on to say that the Ptolemaic theory was the fundamental conception of astronomy; that it guided its scientific development for two thousand years; that it was based on extensive, prolonged, and accurate observations; that it was elucidated and confirmed by mathematics; that it was verified by confirming the power of astronomical prevision; and that the planetary motions were traced and resolved on this theory with great skill and correctness, elaborate tables being constructed, which represented their irregularities and inequalities, so that their future positions could be foretold, and conjunctions, oppositions, and eclipses predicted.
These and similar remarks of the scientific editor would tend to prove that the Congregation of the Holy Office had very good and substantial grounds for condemning the heliocentric theory, and that Galileo was a visionary; for the theory which he impugned was “confirmed by mathematics,” and “verified by confirming the power of astronomical prevision.” We are quite sure, however, that this is not what Mr. Youmans intended to prove; and yet it does not appear why he should fill a column of his magazine with such a panegyric of a defunct theory. We concede—and the fact has never been disputed—that astronomy owes an immense debt to the ante-Copernican investigators for their careful observations and laborious calculations; but we do not see how this has anything to do with Dr. Taylor’s criticism. Had the reverend doctor denied that there was any real knowledge of astronomy before Copernicus, his critic might have been justified in trying to enlighten him about the merits of the Ptolemaic astronomers; but Dr. Taylor had not committed himself on this point, and therefore had no apparent need of being enlightened on the subject. The information, consequently, which Mr. Youmans volunteers to offer him is superfluous, not to say impertinent, and, inasmuch as it professes to be an argument, is a complete failure; for it aims at proving what no one has ever denied.
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.
Dr. Taylor had said, as we have noticed, that the Copernican theory “rests on facts presently occurring before our eyes.” Mr. Youmans answers: “So does the Ptolemaic theory; and not only that, but, if the test is what occurs before our eyes, then the Ptolemaic theory is a thousand times stronger than the Copernican.” If this answer expresses the real opinion of Mr. Youmans, we must conclude that he alone, among physicists, is ignorant of the fact that terrestrial gravitation is modified by the centrifugal force due to the rotation of the earth, and that this fact is established by experiments which “occur before our eyes” when we make use of the pendulum in different latitudes. What shall we say of the aberration of light? Is not this phenomenon a proof of the movement of the earth? Or does it not “occur before our eyes”? Mr. Youmans may say that these facts do not occur before all eyes, but only before the eyes of scientific men. But Dr. Taylor had not maintained that all the facts connected with the Copernican theory occur before all eyes; and, on the other hand, Foucault’s pendulum, even though oscillating before unscientific eyes, makes visible to the dullest observer the shifting of the horizontal plane from its position at a rate proportional to the sine of the latitude of the place, thus showing to the eye the actual movement of our planet. It is true, therefore, that the Copernican theory “rests on facts presently occurring before our eyes.”
But, if the Copernican theory is so obvious, “why,” asks Mr. Youmans, “did the astronomers of twenty centuries fail to discern it? Why could not the divines of Copernicus’ time see it when it was pointed out to them? And why could not Lord Bacon admit it a hundred years after Copernicus?” The why is well known. The Copernican theory was at first nothing more than a hypothesis; and its truth, even after Kepler and Newton, was still in need of experimental confirmation. Had Lord Bacon or the divines of Copernicus’ time seen what we see with our eyes in Foucault’s experiment, there is little doubt that they would have recognized at last the truth of the new theory. But let this suffice about the certitude of the Copernican theory.