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It will be well to pause for a while to consider why the system of Copernicus should now have met with such an increase of opposition, after having been more or less tolerated or ignored for nearly eighty years, during which its most bitter opponents had been not the Roman Church nor the Jesuits, but Luther and other Reformers. It was Luther in particular who insisted on the most literal interpretation of Scripture, and he had certainly not received a liberal education, so that his attitude is quite intelligible, Copernicus being, moreover, a dignitary of the Church to which Luther was opposed.

The tendency of the Reformation, however, was to encourage men to think for themselves, and not to accept blindly the guidance of priests, even in theological matters, and this tendency was bound sooner or later to produce a reaction. It may be that Galileo's ideas, had he lived fifty years earlier, might have received general acceptance before the uneasiness due to the Reformation had created an atmosphere favourable to official Church interference. It is also quite likely that had Galileo been content to adopt Tycho Brahé's system as a working hypothesis, he might have avoided the main difficulty, since the only difference was that involving the earth's revolution round the sun, instead of the sun's round the earth. As a working formula Tycho's system is practically in use now, except that the circular motion, to which Galileo still clung even after Kepler had discovered that the orbits are all elliptical, has been discarded. Copernicus had required a great deal of faith to support his system in the face of enormous practical difficulties. Galileo's telescope had disposed of some of these difficulties, by showing that the stars are much farther off than the planets and the sun, and that certainly some of the planets do revolve about the sun; Jupiter's moons also showed the possibility that the earth might not be the centre of the system, although it clearly has a moon revolving round it.

But what was really required was a proof rather than a plausible hypothesis, and this Galileo considered that he had found in his tidal theory. He had an incomplete grasp of the idea of relative motion, and he thought that as the earth is rotating and revolving round the sun the actual velocity of a point on the surface would be greater when it was turned away from the sun and less when, turned towards the sun. Then assuming that the oceans behaved like water carried in a vessel, he said the water will pile up in the direction of rotation on the earth's surface, where it is moving more slowly, and will also pile up in the opposite direction, where it is moving more quickly, so that there will be high water twice a day, as is actually the case. Many other learned men, with much greater knowledge than was possible in Galileo's day, have completely failed to solve the problem of the tides, so that Galileo's want of success is quite easy to understand. It is not so clear that his opponents understood where his failure lay, but the failure is undeniable, and it seems perfectly clear that if he had produced a real proof of the earth's rotation, the "official" opposition would have been withdrawn. Even Cardinal Bellarmine himself plainly stated that if such proof were forthcorning, it would be necessary to revise the interpretation of some parts of Scripture. Clearly, then, it would have been politic of Galileo to have waited for more convincing proofs before allowing any question of "theology" to be raised. It is easy to say that he did not raise these questions himself, and only responded to challenges, but if his temperament had been less argumentative he could have avoided the plain issue. He considered himself a faithful son of the Church, which required unquestioning obedience; and yet, when his position was pronounced untenable on theological grounds, he was not sufficiently humble to retire gracefully, but maintained his argument and endeavoured to prove that it was not irreconcilable with Scripture. Such an attitude in a layman was bound to raise fierce opposition, apart from the prejudice of certain of the Jesuits. The net result was that the doctrines themselves suffered for the time from his enthusiastic advocacy, and, as we have seen, some works, which might otherwise have been ignored, were placed under the ban of the Inquisition. He himself retired to Florence with an uneasy feeling that he must be more circumspect in dealing with the Copernican system, but hardly aware that anything definitely forbidding it had been said to him.