line had been printed. Had Copernicus never been born there is no doubt that the heliocentric theory would have been announced before the sixteenth century reached its end. Tycho's observations contained it implicitly. It could not possibly have escaped the eager search of Kepler.
Tycho, again, stands as the type of the men who saw that a multitude of accurate places of the heavenly bodies must be accumulated before any adequate theory of their motions could be formulated. The Moors of Spain, the Arabs of Bagdad, the Turkis of Samarkand grasped the same fundamental idea, and other astronomers in Italy and in Germany were in the same path before Tycho.
Who shall say how much Kepler owed to his master, Moestlin, to whom he is never weary of attributing the suggestions which finally culminated in his splendid discoveries?
Galileo's great achievements in astronomy were largely due to the telescope, which he was the first to use, although it was invented by others. His greatest gift to science is his theory of mechanics, but even here Leonardo da Vinci had already gone far on the true way, and his contemporary, Stevinus, developed the whole subject independently and with equal insight. Galileo was surrounded by men of his own class if not of his own stature.
We, in our turn, may accept these four great men—Copernicus, Tycho, Kepler, Galileo—as types; but we must never forget that they did not stand alone. Each one of them shone with brilliant and intrinsic light, but each one was, also, in some degree, the mirror of his age, concentrating and diffusing the reflections of lesser lights by whom he was surrounded. What he received from them as mist, he returned in rain, as has been finely said of the inspiration of an orator by his audience.
Of this group of four, two are veritable epoch-makers—the first and the last. After the book of Copernicus was understood, the world was no longer the same. Its center had been changed. The sun and not the earth ruled our system. The planets and the stars became the sun 's ministers, not ours. Man, nodus et vinculum mundi, was discrowned and disenthroned. It was the doctrine of Copernicus that changed the face of the world.
To realize the momentous change time was necessary. It was Galileo who spoke the emphatic word. The predictions of Copernicus were confirmed by the telescope. The new doctrines were explained and enforced so that no escape was possible. It was Galileo and not Copernicus who convinced the reluctant spirits of his day. The work of one was continued in the other. Not until the time of Newton was the message fully credited. It was not welcomed until our own day.
To the men of the middle ages the world was a little space shut
