showed rotation of that body, the satellites of Jupiter and particularly the phases of Venus, analogous to those shown by the moon, obviously harmonized with the Copernican theory. This implied at least that the planets shone by reflected sunlight, and it had indeed been insisted against that theory that Venus and Mercury under it must show phases till then undiscovered.

In 1632 Galileo published his celebrated Dialogue on the Two Chief Systems of the World, the Ptolemaic and the Copernican, a work comparable in magnitude and importance with Copernicus' Revolutions. In the curious preface he says:

'Judicious reader, there was published some years since in Rome a salutiferous Edict, that, for the obviating of the dangerous Scandals of the present Age, imposed a reasonable Silence upon the Pythagorean Opinion of the Mobility of the Earth. There want not such as unadvisedly affirm, that the Decree was not the production of a sober Scrutiny, but of an illformed passion; and one may hear some mutter that Consultors altogether ignorant of Astronomical observations ought not to clipp the wings of speculative wits with rash prohibitions. My zeale cannot keep silence when I hear these inconsiderate complaints. I thought fit, as being thoroughly acquainted with that prudent Determination, to appear openly upon the Theatre of the World as a Witness of the naked Truth. . . . I hope that by these considerations the world will know that if other Nations have Navigated more than we, we have not studied less than they; and that our returning to assert the Earth's stability, and to take the contrary only for a Mathematical Capriccio, proceeds not from inadvertency of what others have thought thereof, but (had one no other inducements), from these reasons that Piety, Religion, the Knowledge of the Divine Omnipotency, and a consciousness of the incapacity of man's understanding dictate unto us.'

In the first of the four conversations into which the work is divided, the Aristotelian theory of the peculiar character of the heavenly bodies is subjected to destructive criticism, with emphasis on such phenomena as the appearance of new stars, of comets and of sun spots, the irregularities of the moon's surface, the phases of Venus, the satellites of Jupiter, etc.

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'When we consider merely the vast dimensions of the celestial sphere in comparison with the littleness of our earth . . . and then think of the speed of the motion by which a whole revolution of the heavens must be accomplished in one day, I cannot persuade myself that the heavens turn while the earth stands fast.'

Adducing not merely the sun spots themselves, but their rapid variation, he insists that the universe is not rigid and permanent, but constantly changing or, as science has more and more emphasized since his day, passing through consecutive, related phases or evolving.

'I can listen only with the greatest repugnance when the quality of unchangeability is held up as something preeminent and complete in contrast to variability. I hold the earth for most distinguished exactly on account of the transformations which take place upon it.'

He begins to see the fallacy of the objections that if the earth rotated, a body dropped from a masthead would be left behind by the ship and that movable objects could be thrown off centrifugally at the equator. As positive arguments in support of the Copernican system, he urges particularly the retrogressions and other irregularities of the planets, and also the tides.

Of the famous controversy of Galileo with the Inquisition, it may here suffice to quote the judgment of the court (see Appendix):

"The proposition that the sun is in the centre of the world and immovable from its place is absurd, philosophically false and formally heretical; because it is expressly contrary to the Holy Scriptures,' etc. and a passage from the biographer already cited at so much length :

For over fifty years he was the knight militant of science, and almost alone did successful battle with the hosts of Churchmen and Aristotelians who attacked him on all sides one man against a world of bigotry and ignorance. If then, . . . once, and only once, when face to face with the terrors of the Inquisition, he, like Peter, denied his Master, no honest man, knowing all the circumstances, will be in a hurry to blame him.

Of Galileo's still more remarkable services to physics and dynamics, something will be added in a later chapter.

MEDICAL AND CHEMICAL SCIENCES. - These were still at the low medieval level. There was as yet no scientific medicine, and no chemistry but alchemy, which was now in its final stage, iatro (medical) chemistry. Here one great name is that of Paracelsus (1493-1541), erratic and radical Swiss physician and alchemist, whose chief merit is his courage in opposing mere authority in science, and whose influence long after caused "salt, sulphur, and mercury" to be highly regarded and carefully studied. He also introduced and insisted upon the importance of antimony as a remedy, and is said to have been the first to use that tincture of opium which is still known by his name for it; viz. laudanum. Paracelsus, on the other hand, in spite of the fact that he was a popular surgeon, rejected the study of anatomy, taught medical knowledge through scanning of the heavens, and considered diseases as spiritual in origin. “The true use of chemistry," he said, "is not to make gold but to prepare medicines."

Another name worthy of remembrance in the chemistry of the sixteenth century is that of Landmann (Latin, Agricola) whose great work on Metallurgy (De Re Metallica, 1546) is the most important of this period, and who must also be regarded as the first mineralogist of modern times.

ANATOMY. VESALIUS.-Hardly less important, meantime, than the studies of Copernicus, Tycho Brahe, Galileo and Kepler upon the heavenly bodies were those of the Belgian anatomist, Andreas Vesalius, upon the human body. For more than 1000 years there had been almost no progress in anatomy or medicine, Hippocrates and Galen being still regarded as the final authorities in these matters up to the middle of the sixteenth century. Vesalius (1514-1564), born in Brussels and educated in Paris, was the first in modern times to dissect the human body, and to publish excellent drawings of his dissections. It was said that he opened the body of a nobleman before the heart had entirely ceased beating, and thereby incurring the displeasure of the Inquisition, was sen