CHAP. IX. 



Of Thunder^ and Earthquakes; of the Virtue of 

 the Magnet ; of the Ebbing and Flowing of the 

 Sea / and of the Source of Rivers.. 



I. J[ GO on to some articles of natural philosophy, 

 where I shall endeavour to shew the conformity there 

 is between the ancients, and some of our most cele- 

 brated philosophers. It is evident that the causes of 

 thunder, earthquakes, the attractive force of the load- 

 stone, the ebbing and flowing of the sea, and the re. 

 turn of rivers to their source, were not hid from the 

 former; nor was it their fanlt, that the sentiments 

 they so long ago held on these subjects, were either 

 not adopted or not till very lately. It ought not to 

 ba objected here, that the diversity of opinions among 

 them was so great, that it Avas difficult to determine 

 which to choose ; unless, at the same time, it be ac- 

 knowledged, that the same holds true with respect to 

 the equal variety that reigns at present among us. 

 It is not long ago, that two or three different sets of 

 notions were raised up against those of Sir Isaac 

 Newton, respecting colours; but that did not impede 

 the triumph of his system, nor strip him of the glory 

 of having proposed, what beyond all others, was most 

 just and solid. 



2. The moderns are divided into two opinions as to 

 what occasions thunder ; some of them assigning the 

 cause of it to inflamed exhalations, rending the clouds 

 wherein they are confined ; others ascribing it to the 

 shock that happens between two or more clouds, 



