Page:Philosophical Transactions - Volume 003.djvu/184

 had an extraordinary Trayn, sometimes 45, 60, 75, yea 104 degr, long, as also that for some time it shone all night, and now and then seem'd to break out into Lightning, To all which he adds the Observations of the Comets seen A. 1647, 1652, 1661, 1664, 1665, of which the last four were diligently observ'd and are exactly described by himself.

As for the Theory, whereby the Author renders an Account of all the Phenomena of Comets, he supposeth, that they all move in a Straight Line, by which supposition (first suggested by Kepler) and no other, that he can imagine, he esteems that all the Appearances of them, how insoluble soever else they seem, may very easily be explicated, especially supposing the Sun in the Center of the Universe, and the Annual motion of the Earth; though he suggests also away of saving the said Rectilinear motion even without destroying the system of Ptolomy. But yet he would not be understood so strictly in asserting that streight motion, but that Comets may more or less deviate from that streightness, both in appearance, and really; the former arising from the various sight of them, and their various distance from the Earth and the Sun, and the Annual motion of the Earth, the latter, from the matter of their Bodies and Nucleus's (as he calls the substance of their Head) not increasing nor decreasing uniformly on all sides. To which he adds the consideration of a motion impress'd, and that of an Inclination of the Cometick Disk to the Sun, as two other Causes, why Comets may now and then, especially about the beginning and end of their appearance, somewhat digress from their streight course. Where he alledges, that he hath much laboured to give an account of Comets by a Circular motion, but could not possibly satisfie himselfe in it, nor answer the Phænomena of most, though perhaps that Hypothesis may serve to salve some of them.

But then, to explaine that Trajectory rectilinear motion, he subjects the Comet of A. 1652, to a very rigid calculus, to shew, how that line is to be delineated, and how that way is applicable to all other Comets.

Further, to render a Cause of this motion, he supposeth, that, as all Celestial Bodies move about their Axes, their Atmosphere wheeling perpetually round about with them; so the matter, Rh