Mijcellanea Curio fa. 1 1 



Now, the Latm Retina of an Elltpfis, is to the 

 LatasRettHw of a Parabola, which has the fame 

 Diftance in its Perihelium 5 as the Diftance in 

 the Afhelimn in the Ellipfis, is to the whole 

 Axis of the Elliffis, And the Velocities are 

 in a Subduplicate Ratio of the fame : Where- 

 fore in very Excentrick Orbits this Ratio comes 

 very near to a Ratio of Equality • and the very 

 fmall Difference which happens on Account of 

 the greater Velocity in the Parabola, is eafily 

 compenfated in determining the Situation of 

 the Orbit. The principal life therefore of 

 this Table of the Elements of their Motions, 

 and that which induced me to conftruft it, is, 

 That whenever a new Comet fball appear, we 

 may be able to know, by comparing together 

 the Elements, whether it be any of thoie which 

 has appear'd before, and confequently to deter- 

 mine its Period, and the .Axis of its Orbit, 

 and to foretell its Return. And, indeed, there 

 are many Things which make me believe 

 that the Gomet which Apart obferv'd in the 

 Year 1531. was the fame with that which 

 Kepler and Loiigomontanm took Notice of and 

 defcrib'd in the Year 1697. and which 1 my felf 

 have feen return, and obferv'd in the Year 1682. 

 All the Elements agree, and nothing feems to 

 contradift thismy Opinion, befides the Inequali- 

 ty of the Periodick Revolutions: Which Inequa- 

 lity is not fo great neither, as that it may not be 

 owing to Phyilcal Caufes. For the Motion of 5^ 

 inrn\% fo difturbed by the reft of the Planets, e- 

 fpecial]y7«/>/w,that the Periodick Time of that 

 Planet is uncertain for fome whole Days to- 

 gether. How much more therefqre will a Co- 

 met be fubjeft to fuch like Errors, which rifes. 

 A 3 



