The very triumphs of Galileo and his telescopic discoveries were the causes, to a great extent, of those ceaseless and relentless persecutions which were to restrict his labours and embitter his life. The Aristotelians perceived with rage and terror the revolutionary discoveries of this dangerous innovator were surely, if slowly, gaining ground. Every one of them, with its inevitable logical consequences, pulled down some important stone in the artistic structure of their views of nature; and unless some measures were taken to arrest the demolition, it was clear that the venerable edifice must fall and bury the inmates beneath the ruins. This must be averted at any price, even at the price of knowledge of the acts of nature. If Galileo’s reformed physics offered no point of attack, his astronomy did; not indeed in the honourable contest of scientific discussion, but by bringing theology into the field against science. Galileo had never openly proclaimed his adoption of the earth’s double motion, but the demonstration of his telescopic observations alone sufficed to make it one of the burning questions of the day. What were the phases of Venus and Mercury, the motions of the solar spots, and above all Jupiter and his moons, this little world within our large one, as Galileo afterwards called it himself,[75] but telling proofs of the truth of the Copernican theory? The question of the two systems had been hitherto an exclusively scientific one. How else could the famous philosopher and astronomer Nicholas of Casa, who taught the double motion of the earth in the fifteenth century, have gained a cardinal’s hat? How could the German, Widmanstadt, have explained his theory, which was based upon the same principles, to Pope Clement VII. in 1533? How could learned men like Celio Calganini, Wurteis, and others, have given public lectures on the subject in Italy in the second half of the sixteenth century? Neither Casa, however, nor Widmanstadt, Calganini, Wurteis, nor even Copernicus, had ventured openly to declare war with the school of Aristotle, nor to overthrow by the crushing evidence of experiment the dogmas of natural science based upon philosophy and _a priori_ arguments alone. These learned men had been tolerated because they fought with the same weapons as the followers of Ptolemy, logic and philosophy. They did not possess the powerful lever of direct evidence, because they were not acquainted with the telescope. But Galileo, with his fatal system of demonstration by observation of nature, was far too dangerous a foe. Peripateticism was no match for the home thrusts of arguments obvious to the senses, and its defenders were well aware that if they would not yield their position they must call in some other ally than mere science. And they adopted the means best adapted for putting a temporary drag on the wheels of truth, and for ruining Galileo; in order to prop up the