Prussia. During thirty-six of the seventy years that were allotted to him he studied the motions of the planets. Throughout a large part of his life he held high ecclesiastical rank as canon of Warmia, and had leisure for his favorite investigations. The variations in the brightness of Mars in different parts of its orbit were so great as to lead him to think that the earth could not be the center about which Mars revolved. The results of his meditations are set forth in the following translation of his own words :

And I too, on account of these testimonies, began to meditate upon the movement of the earth, and though that theory seemed absurd, I thought that as others before my day had devised a system of circles to account for the motion of the stars, I also might endeavor, by supposing that the earth moved, to find a more satisfactory scheme of the movements of the heavenly bodies than that which now contents us. After long research I have become convinced that if we assume the revolution of the earth to be the cause of the wanderings of the other planets, observation and calculation will be in better agreement. And I doubt not that mathematicians will be of my opinion, if they will take pains to examine carefully and thoroughly the demonstrations to be given in this book.

The new

theory.

The new vs. the

Copernicus broke with the Ptolemaic theory at two points. He placed the sun in the center of the planetary old. system, and explained the diurnal rotation of the heavens by the revolution of the earth on its axis. For a long time he hesitated about publishing the new doctrines, knowing that they would at once make him a target for the ridicule and abuse of the unthinking and of the narrow-minded.

His work is

The insistence of his warmest friends, particularly of the bishop of Culm, finally led to the publication of his published. great work, which was entitled "De Revolutionibus Orbium Cœlestium." It may well be called the Magna

Its importance. Charta of astronomical science. Copernicus did not live to see the reception which was accorded it; the first copy, fresh from the press, was placed in his hand only a few hours before his death. In one important particular Copernicus failed to break with Ptolemy; he still retained the system of epicycles, but the innovations which he introduced simplified it greatly. The new system was soon to be put to a much more searching test than Ptolemy's had been subjected to. In 1546, three years after the death of Copernicus, there came into the family of a Danish nobleman a son, who afterward became the famous Tycho Brahé. In those days it was little

Tycho Brahé.

An eclipse.

short of a misdemeanor for a member of an aristocratic family to engage in scientific researches; to hunt animals and to kill men according to the canons of war were the proper pursuits. The young noble was therefore destined for the army.

When but fourteen years of age Tycho's curiosity was aroused by the occurrence of an eclipse. From that time forth his mind was with the stars. Sent to Leipzig to study law, he could not be induced to devote himself to it; his money was spent for astronomical books and

instruments, and his time was largely engrossed with observations of the stars. In 1563 he observed a conjunction of Jupiter and Saturn, which he thought to be the cause of the Great Plague. As the Copernican tables did not give the time of the conjunction accurately he resolved to make new ones. He constructed instruments of large size, and began to observe with fresh vigor. The king heard of his doings, and offered him a site for an observatory, £20,000 for the building, and a life pension of £400. The observatory, which was called Uranienburg (the Castle of the Heavens), was Uranienburg. erected on the island of Huen, near Copenhagen. It was stocked with the largest and finest instruments which the mechanics of that day could build. For twenty years he worked with the utmost ardor, accumulating a vast store of observations of far greater accuracy than any which had been made previously. Of the subsequent death of his patron, his own impoverishment and virtual banishment, we may not give the details. On October 24, 1601, he died, after a painful illness, during which he frequently called out, "Ne frustra vixisse videar" (May I not seem to have lived in vain!). Two years before Tycho's death, Johann Kepler Kepler. became his pupil. Tycho was one of the greatest of observers, but his pupil was preeminent as a theorist. Taking up Tycho's observations of Mars he endeavored to discover the laws of the planet's movement. Hypothesis after hypothesis was tried and rejected; at one moment he was at the summit of hope; at another he was in the depths of disheartenment. Struggling with indomitable perseverance against sickness, poverty, and misfortune, harassed by domestic troubles, and hampered at every turn, he pressed on through weary years to final victory.

His exultation.

Galileo.

areas in equal

times.

Law III. The

squares of the times of revolution of any two planets are to each other as the cubes of their mean distances

from the sun.

Upon the dis

covery of the third law his exultation knew no bounds, as the following exclamation shows:

Nothing holds me: I will indulge in my sacred fury: I will triumph over mankind by the honest confession that I have stolen the golden vases of the Egyptians to build up a tabernacle for my God far away from the confines of Egypt. If you forgive me, I rejoice: if you are angry, I can bear it: the die is cast, the book is written, to be read either now or by posterity, I care not which it may well wait a century for a reader, as God has waited six thousand years for an observer.

While Kepler was making his immortal studies in theoretical astronomy, the science of observation took a tremendous stride. Galileo, then a professor in the University of Padua, heard that a Dutch spectacle-maker

had found a combination of glasses through which the weathercock on the church spire looked larger. Being familiar with the laws of optics he began to ponder over the matter. All night long he sat in a brown study; by morning the solution came, and he soon had an old organ pipe with a glass at each end, which was the forerunner of the great telescopes of our day. The Senate doubled his salary, and he went at telescope-making in earnest; having completed one which magnified thirty times he began to explore the heavens.

The moon displayed to him the rocky ramparts and battlemented crags of her mountains. The Milky Way was resolved into countless stars;

"Infinity's illimitable fields,

Where bloom the worlds like flowers about God's feet."

Jupiter was found to be attended by four moons, the entire system being a miniature of the solar system. The motions of these

bodies powerfully confirmed the theories of Copernicus. The surface of the sun was seen to be marred by spots. Venus became a waxing and waning crescent.

The Aristoteli

ans were con

founded again and

again. But they

had their revenge upon this pestilent fellow, who was turning the world of natural philosophy upside down.

Discoveries.

The

The hand of the Inquisition was laid upon him. But Inquisition.