166 FRAGMENTS OF SCIENCE 



Gospels, the heliocentric doctrine, which he knew to be 

 true. After Galileo came Kepler, who from his German 

 home defied the ultramontane power. He traced out from 

 pre-existing observations the laws of planetary motion. 

 Materials were thus prepared for Newton, who bound those 

 empirical laws together by the principle of gravitation. 



4 



In the seventeenth century Bacon and Descartes, the 

 restorers of philosophy, appeared in succession. Differ* 

 ently educated and endowed, their philosophic tendencies 

 were different. Bacon held fast to Induction, believing 

 firmly in the existence of an external world, and making 

 collected experiences the basis of all knowledge. The 

 mathematical studies of Descartes gave him a bias toward 

 Deduction; and his fundamental principle was much the 

 same as that of Protagoras, who made the individual man 

 the measure of all things. "I think, therefore I am," said 

 Descartes. Only his own identity was sure to him; and 

 the full development of this system would have led to an 

 idealism, in which the outer world would have been re- 

 solved into a mere phenomenon of consciousness. Gas- 

 sendi, one of Descartes 's contemporaries, of whom we 

 shall hear more presently, quickly pointed out that the 

 fact of personal existence would be proved as well by ref- 

 erence to any other act, as to the act of thinking. I eat, 

 therefore I am, or I love, therefore I am, would be quite 

 as conclusive. Lichtenberg, indeed, showed that the very 

 thing to be proved was inevitably postulated in the first 

 two words, "I think"; and it is plain that no inference 

 from the postulate could, by any possibility, be stronger 

 than the postulate itself. 



