108 DISSERTATION SECOND. [parti. 



undisputed author. It is by following his reasonings, and 

 by pursuing the train of his thoughts in his own elegant, 

 though somewhat diffuse exposition of them, that we be- 

 come acquainted with the fertility of his genius, with the 

 sagacity, penetration, and comprehensireness of his mind. 

 The service which he rendered to real knowledge, is to 

 be estimated not only from the truths which he discovered, 

 but from the errours which he detected, — not merely from 

 the sound principles which he established, but from the 

 pernicious idols which he overthrew. His acuteness was 

 strongly displayed in the address with which he exposed 

 the errours of his adversaries, and refuted their opinions, 

 by comparing one part of them with another, and proving 

 their extreme inconsistency. Of all the writers who have 

 lived in an age, which was yet only emerging from igno- 

 rance and barbarism, Galileo has most entirely the tone 

 of true philosophy, and is most free from any contamina- 

 tion of the times in taste, sentiment, and opinion. 



The discoveries of this great man concerning motion 

 drew the attention of philosophers more readily, from the 

 circumstance that the astronomical theories of Copernicus 

 had directed their attention to the same subject. It had 

 become evident, that the great point in dispute between 

 his system and the Ptolemaick must be finally decided by 

 an appeal to the nature of motion and its laws. The great 

 argument to which the friends of the latter system naturally 

 had recourse was the impossibility, as it seemed to them 

 to be, of the swift motion of the earth being able to exist, 

 without the perception, nay, even without the destruction, 

 of its inhabitants. It was natural for the followers of Co- 

 pernicus to reply, that it was not certain that these two 

 things were incompatible ; that there were many cases in 

 which it appeared, that the motion common to a whole 

 system of bodies did not affect the motion of (hose bodie? 



