tier, iv.] DISSERTATION SECOND. 



149 



might be imagined. The philosophy of Descartes could 

 explain all things equally well, and might have been ac- 

 commodated to the systems of Ptolemy or Tycho, just as 

 well as to that of Copernicus. It forms, therefore, no link 

 in the chain of physical discovery ; it served the cause of 

 truth only by exploding errours more pernicious than its 

 own ; by exhausting a source of deception, which might 

 have misled other adventurers in science, and by leaving 

 a striking proof, how little advancement can be made in 

 philosophy, by pursuing any path but that of experiment 

 and induction. Descartes was, nevertheless, a man of 

 great genius, a deep thinker, of enlarged views, and entire- 

 ly superiour to prejudice. Yet, in as far as the explanation 

 of astronomical phenomena is concerned (and it was his 

 main object,) he did good only by showing in what quarter 

 the attempt could not be made with success ; he was the 

 forlorn hope of the new philosophy, and must be sacrificed 

 for the benefit of those who were to follow. 



Gassendi, the contemporary and countryman of Descar- 

 tes, possessed great learning, with a very clear and sound 

 understanding. He was a good observer, and an enlight- 

 ened advocate of the Copernican system. He explained, 

 in a very satisfactory manner, the connexion between (he 

 laws of motion and the motion of the earth, and made ex- 

 periments to show, that a body carried along by another 

 acquires a motion which remains after it has ceased to be so 

 carried. Gassendi first observed the transit of a planet over 

 the disk of the sun, — that of Mercury, in 1631. Kepler 

 had predicted this transit, but did not live to enjoy a 

 spectacle which afforded so satisfactory a proof of the 

 truth of his system, and of the accuracy of his astronomical 

 fables. 



The first transit of Venus, which was observed, hap- 

 pened a few years later, in 1639, when it was seen in En- 



19 



