He puts it out of doubt, that they are in the _Sky_ it self, producing reasons for it that are very considerable, and alledging amongst others, That the _Parallaxes_ doe clearly evince it, which he finds far less in Comets, then in the _Moon_, yea then sometimes in the _Sun_ it self. Where he also represents, That he hath deduced the _Horizontal Parallax_ of this very Comet from one onely Observation, made _Feb._ 4. _st. n._ by which he found, That then it was distant from the Earth 5000 Semidiameters of the same, or 4300000 _German_ miles. From this distance from the earth, he deduces, That on that Day when it was so remote from the Earth, its true _Diameter_ was 2560 _German_ miles, which is three times bigger then the Diameter of the Earth, and almost six times bigger then that of the Moon, whose Diameter, according to his _Theory_, is 442 _German_ miles. He finds the _Matter_ of Comets to be in the _AEther_ it self, making the _AEther_ and the _Air_ to differ only in purity, and esteeming, That the _Planets_ do emit their Exhalations, and have their _Atmospheres_ like unto our Earth. Where he affirms, That the Sun alone may cast out so much Matter at any time in one year, as that thence shall be produced not one or two Comets, equallizing the Moon in Diamiter, but very many; which if so, what contribution may not be expected from the other Planets? Of this Cometical Matter, he thinks, That first it is by little and little gathered together, then coagulated and condensed, and thereby reduced to a less Diameter; but then, after a while it resolves again, and grows dilute and pale, and at last is dissipated. And accordingly he affirms, That he hath observed the Head of this Comet at first more confused, thin and pale, afterwards clearer and clearer. {107} He conceives, That all Comets do respect the _Sun_ as their _King_ and _Centre_, as _Planets_ do, making them a kind of _Spurious Planets_, that emulate the _true_ ones in their Motion almost in all things. The _Train_, he makes nothing else but the Beams of the Sun, falling on the head of the Comet, and passing through the same, refracted and reflected. And amongst his _Observations_ and _Schemes_ of this Comet, there occurs one, wherein the Tail is _curve_, so seen by him _Decemb._ 11/21. He assigns the causes why the Trains do so much vary, and shews also, on what depends their length. Whether the _same_ Comet returns again, as the Spots in the Sun? and, whether in the time of great _Conjunctions_ they are more easily generated? and whether they can be certainly foretold? with several other Inquiries, he refers for to his _great Book_.