A HISTORY OF SCIENCE 



was originally named, Johann von Kappel, was one 

 of the most speculative astronomers of any age. He 

 was forever theorizing, but such was the peculiar 

 quality of his mind that his theories never satisfied 

 him for long unless he could put them to the test of 

 observation. Thanks to this happy combination of 

 qualities, Kepler became the discoverer of three fa- 

 mous laws of planetary motion which lie at the very 

 foundation of modern astronomy, and which were 

 to be largely instrumental in guiding Newton to his 

 still greater generalization. These laws of planetary 

 motion were vastly important as corroborating the 

 Copernican theory of the universe, though their position 

 in this regard was not immediately recognized by con- 

 temporary thinkers. Let us examine with some detail 

 into their discovery, meantime catching a glimpse of 

 the life history of the remarkable man whose name 

 they bear. 



JOHANN KEPLER AND THE LAWS OF PLANETARY MOTION 



Johann Kepler was born the 2yth of December, 

 1571, in the little town of Weil, in Wurtemburg. He 

 was a weak, sickly child, further enfeebled by a severe 

 attack of small-pox. It would seem paradoxical to 

 assert that the parents of such a genius were mismated, 

 but their home was not a happy one, the mother being 

 of a nervous temperament, which perhaps in some 

 measure accounted for the genius of the child. The 

 father led the life of a soldier, and finally perished in the 

 campaign against the Turks. Young Kepler's studies 

 were directed with an eye to the ministry. After a 

 preliminary training he attended the university at 



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