24 POPULAR SCIENCE MONTHLY. 



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 multi- 

 tude 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 Ger- 

 many were in the same path before Tycho. 



Wlio 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 inde- 

 pendently 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 in- 

 trinsic 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. Wliat 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 



