jMifcettanea Curio fa. 1 1$ 



may find it at the End of the Third Book of 

 Sir Ifaac Newtonh Principles of Natural Phi- 

 lofophy, entituled De Syftemate Mundi, in the 

 Words of its renowned Inventor. Which 

 have lince been niore fully explained by my very 

 worthy Collegue Dr. Gregory ? in his Learned 

 Work of Aftronomia Phyfica & Gepmetrtc-a. 



One Thing more perhaps it may not be im- 

 proper or nnpleafant to advertife the Aftrono- 

 mical Reader j That fome of thefe Comets 

 have their Nodes fo very near the Annual Orb 

 of the Earth, that if it fhall fo happen, that 

 the Earth be found in the Parts of her Orb 

 next the Node of fuch a Comet, whillt the^Co- 

 met pafles by j as the apparent Motion of the 

 Comet will be incredibly fwift, fo its Parallax 

 will become very fenfible; and the Proportion 

 thereof to that of the Sun will be given. Where- 

 fore fuch Tranfits of Comets do afford us the 

 very belt Means, though they feldom happen, 

 to determine the Diftance of the Sun and 

 Earth : Which hitherto has only been attempt- 

 ed by Mars in his Oppoiition to the Sun - ? or 

 elfe Vennt in Perlgao ; whefe Parallaxes though 

 triple to that of the Sun, are fcarce any ways 

 to be perceived by our Inftruments \ whence 

 we are ftill in great Uncertainty in that Affair. 

 This ufe of Comets was the ingenious Thought 

 of that excellent Geometrician Mr. Nicolas 

 Facio. Now the Comet of 1472, had a Pa- 

 rallax above Twenty times greater than the 

 Sun's. An,d if the Comet of 161 8, had come 

 down, about the Middle of March, to his de- 

 fending Node: Or if that of 1684, had arr : ~ 

 ved a little fooner at its aft ending Node-, 

 they would h^ve been yet much nearer the 



Earth, 



