274 ANTIENT METAPHYSICS. Book 11. 



hypothcfes, which, in every refpea, appear to be altogether unnecef- 

 fary *. 



And, indeed, I cannot help thinking, that Sir Ifaac went a little out 

 of his province, as a geometer and mechanic, when he meddled at all 

 with the caufe or principle of motion of the celeQial bodies ; for ma- 

 thematics can do no more than calculate and compare together motions 



and 



• As the circular or elliptical motion Is proved, by fa6l and obfcrvation, to be re- 

 folvable into two motions, one from the cent-r, the other to it, 1 thought that there 

 muft be fome reafon for this, and that the reafon was no other than the nature of 

 the motion. And, as it is demonllratcd, and was known even to the antients, that 

 a motion in a ftraight line, as Hmple as any motion can be conceived to be, is never- 

 thelefs refolvable into the two motions mentioned in the text, I fufpe£led that it was 

 likewife demonflrable a priori, that the circular or elliptical motion was refolvable 

 into the centripetal and centrifugal motions ; and, accordingly, upon inquiry, I am 

 iniormud tliat bir Ifaac has adlually deinonllrated it to be fo. Now, this being the 

 cafe, it appears that thofe who maintain that the orbicular motion is necefTarily com- 

 pofed of the centripetal and centrifugal motions, are only miftaken in fuppofing that 

 it is actually focompofed ; and, therefore, that it has a double tendency, to the centre 

 and from it. Whereas, if they had faid, that the motion, though perfedly fimpjc in 

 itfelf, as fimple as the motion in a flraight line, was ncverthekfs compofed oi the cen- 

 tripetal and centrifugal motions, in fo far as to be refolvable into thefe, it would have 

 been no more than the truth, and would have ferved every purpoie of the philofophy 

 they meant to dctentl. 



It^'may beobjeftcd, that 1 have taken no notice of Sir Ifaac's fyftem of the tides, 

 which he explains by his grand principle of gravitation and attraction : But, if there 

 be no fuch thing as gravitation in the celeftial regions, as 1 have endeavoured to fhow, 

 and, if we have no conception of body operating upon body by attradion, or any orher 

 way than in contaft, it neccilarily follows, that the movement of the tides muft be 

 accounted for, like every other movement that is not mechanical, from the i/nmcdiate 

 operation ot mind. But it muft be fuppofcd, that the mind which move* the waters, 

 will do It regularly, and in conformity to the motions of the moon, more or lefs, as 

 fhe is nearer to, or farther from the w.;ters ; for, as 1 have obierved above, it would 

 be anomalous, and out of the order oi nature, if two bodies, fo related as the moon 

 and our i?rth, the one iurrounding, the other furrounded, fliould not have an in- 

 fluence upon one another, and a mutual lympathy. 



