died at that place in 1382. In a translation of the four books of Aristotle, Oresme commented upon Aristotle's contentions for an immovable, central earth, gave numerous reasons and arguments against this hypothesis, and showed it to be unsound. The work in which this was done was never published, though several manuscript copies exist. Probably other thoughtful inquirers had the same dissatisfaction with the theory of a fixed central earth, but were unwilling to publish any criticism of what was then the orthodox view. It was perhaps fortunate for Copernicus himself that the work in which he finally dethroned the earth from the position it had held for so long and, following Aristarchus, made the sun the centre of our system, was not published to the world until he was on his death-bed in 1543.

In the plan of the solar system conceived by Copernicus, the planets Mercury and Venus are nearer the sun than is the earth; and in the course of their revolutions around the body to which they owe their light they must, therefore, exhibit phases like those through which the moon passes monthly. Copernicus knew that these phases were a consequence of his theory, and predicted that they would be found to exist. One of the first uses to which Galileo put his telescope in 1610 was the observation of Venus, and he wrote a full account of the changes seen by him in the appearance of the planet, from the fully-illuminated disc to the crescent form and then through the half-moon aspect to full again. The discovery of these phases provided an unanswerable argument for the Copernican theory.

From the observation of these wonderful phenomena we are supplied with a determination most conclusive, and appealing to the evidence of our senses, of two very important problems, which up to this day were discussed by the greatest intellects with different conclusions. One is that the planets are bodies

not self-luminous (if we may entertain the same views about Mercury as we do about Venus). The second is that we are absolutely compelled to say that Venus (and Mercury also) revolve round the sun, as do also all the rest of the planets. A truth believed, indeed, by the Pythagorean school, by Copernicus, and by Kepler, but never proved by the evidence of our senses as it is now proved in the case of Venus and Mercury. Galileo.

The discoveries made by Galileo with his telescope excited the hostility of the expounders of Aristotelian philosophy; and they supported the Copernican doctrine to such an extent as to bring him under the ban of the Romish Church. He was denounced to the Inquisition in 1612, but it was not until 1633 that proceedings were taken which resulted in the observer of seventy years of age being bound by oath to abjure the doctrine" that the sun is at the centre of the universe and is immovable, and that the earth is not the centre and is movable,' and being treated as prisoner for the last nine years of his life. During this time, in his exile at Siena and Arcetri, his interest in science never waned, despite his infirmities, and he devoted himself to dynamical problems on which he was still at liberty to express opinions.

The Copernican doctrine was believed to be contrary to Holy Scripture, and therefore Galileo was compelled to renounce it and to do penance for teaching it. Whatever was in his mind as he rose from his knees before the ten Cardinals in the Convent of Minerva, Rome, on June 22, 1633, we cannot know, but it is unlikely that he muttered Eppur si muove "—and yet it movesas is related in the familiar anecdote associated with his abjuration.

The action of the Inquisition in forcing Galileo to deny the evidence of his own senses cannot be condemned too strongly; but the fact that the Church of

Rome was responsible for the recantation may almost be said to have been incidental. Had the Salvation Army or a council of politicians possessed the same powers in those days, they would probably have been just as active in crushing what was believed to be a pestiferous doctrine for which the people were not prepared and which was, therefore, a danger to the State. We need not go back three hundred years to find scientific workers who have been deprived of their posts, or whose careers have been ruined, because of their convictions. The man who to-day dared to teach doctrines so revolutionary as those held by Galileo, so opposed to conceptions of what is sacred, and contrary to what public opinion considers to be true, may not be tortured or imprisoned, but he would assuredly suffer social ostracism and would lose position and friends as sadly as Galileo did in his old age.

Copernicus put forward his doctrine of the arrangement and movements of bodies in the solar system hesitatingly, and merely as a hypothesis by which the different positions of the sun and planets as seen from the earth could be explained much more simply than on a system involving an immovable earth in the centre of the universe. Of a different type of mind was Giordano Bruno, who had arrived at a like conception of the cosmic system by intuition, and not only went beyond Copernicus in his ideas but also in his fearless advocacy of them. Thirty-three years before Galileo had been brought before the Inquisition, Bruno had declared to the same body his philosophical creed in unmistakable terms.

I believe in an infinite universe, the effect of the infinite divine potency, because it has seemed to me unworthy of the divine goodness and power to create a finite world, when able to produce