j'4 ESSAYS AND OBSERVATIONS 



er given to matter to continue itfelf iflt 

 motion. A piece of matter cannot move 

 in a ftreight line, without one or other of 

 thefe caufes ; and as little in a circle. 

 Therefore, to make this fuppofed fluid 

 to circulate about the fun, one or other 

 of thefe caufes mufl: operate j and one of 

 other of thefe caufes is fufficient to ac- 

 count for the motion of the planets, with- 

 out necellity of inventing a fluid to pro- 

 duce the effedl. Ees Cartes, therefore^ 

 and his followers are guilty of the fame 

 fort of abfurd reafoning, for which we 

 juftly laugh at the poor Indian, who was 

 forced to invent an overgrown elephant 

 to reft the earth upon, and an overgrown 

 crab to be a footftool to the elephant. 



Whether the fame inconfiftency of 

 a body adling where it is not, has moved 

 our Britifli philofopher to invent an sethe- 

 rial medium much rarer than air, as the 

 caufe of gravitation, I cannot fay. In the 

 twenty-firfl: query, at the end of his Optics, 

 he obferves, " that this medium is much 

 " rarer within the denfe bodies of th6 

 " fun, flars, planets, and comets, than in 



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