THE BELFAST ADDRESS. 155 



his knees, with his hands upon the holy 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 gravi- 

 tation. 



4. 



In the seventeenth century Bacon and Descartes, 

 the restorers of philosophy, appeared in succession. 

 Differently 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 know- 

 ledge. The mathematical studies of Descartes gave 

 him a bias towards 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 resolved into a mere phe- 

 nomenon of consciousness. Gassendi, 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 reference 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, 

 6 1 think ; ' and it is plain that no inference from the 

 postulate could, by any possibility, be stronger than the 

 postulate itself. 

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