He observes this Comet not before _Decemb._ 4/14, (though he conceives it might have been seen since _Novemb._ 23 _st. n._) & he saw it no longer then _Feb._ 3/13: though several others have seen it both sooner, and later: and though himself continued to look out for it till _March_ 7. _st. n._ but fruitlesly, whereof he thinks the reason to have been its too great distance and tenuity. {105} He finds, its apparent Motion was not made in a _Just_ great Circle, but deviated considerably from it; and conceives, that every Comet falls to this deviation, when this apparent Motion grows slow, and the Star becomes Stationary (which, as he saith, it doth in respect of the _Ecliptick_, not its own _Orbite_,) Here he observes, That from _Decemb._ 8/18, to _Decem._ 30. _Jan._ 9. its course was almost a great Circle: but that _then_ it began to deflect from that Circle towards the _North_; so that afterwards, with a very notable and conspicuous Curvity, it directed its course towards _Primam Arietis_: Of which deflection, he ventures to assign the cause from the Cometical Matter, the various position and the distance of the Comet from the Earth and the Sun, the annual Motion of the Earth, and the impressed Motion, and the inclination of the _discus_ of the Cometical Body. He is pretty positive, that without the _annual Motion_ of the _Earth_, no rational Account can be given of any Comet, but that all is involved with perplexities, and deform'd by absurdities. He inquires, since all Comets have the peculiar _Ingenite_ Motion, what kind of Line it is, they describe by that Motion of their own? whether circular, or streight, or curve, or partly streight and partly curve? And if curve, whether regular or irregular? if regular, whether Elliptick, or Parabolar, or Hyperbolical? He answers, That this Motion is _Conical_; and judgeth, that by the _Conick_ path all the _Phaenomena_ of Comets can, without any inconveniency, be ready solved; even of that, which (by History) in fifty daies, passed through more then the 12 Signs in the _Zodiack_: And of that, which in two daies ran through eight Signs: and of another, which in 48 daies posted through all the Signs, _contra seriem_. Which how it can be explicated upon the supposition of the Earths standing still, and upon the denying of the annual Motion thereof, he understands not at all. {106} He refers to his _Cometography_ these Disquisitions: whether all Comets (in their innate Motion) move equal _spaces_ in equal _Times_? which is the swiftest, and which the slowest Motion they are capable of? what the cause of this acceleration and retardation of their true Motion?