Observatio & demonstratio cometae aetherei, qui anno 1577 et 1578 constitutus in sphaera veneris, apparvit, cum admirandis eius passionibus, varietate scilicet motus, loco, orbe, distantia à terrae centro, &c. adhibitis demonstrationibus geometricis & calculo arithmetico, cuiusmodi de alio quoquam cometa nunquam visa est

since it cannot bear delay. But in the meantime, from the writings of many which were scattered in public and also reached me, I understand that others think very differently about the region of this Comet and drag it down into the lower world, even though I could never persuade myself that this same thing was not likewise noticed and observed even by naked ocular inspection and reasoning by so many astronomers under a most clear sky, which is often very convenient for this business. Here, however, I pondered with myself how easily it might happen that the authority of others (even if they are mistaken in their opinion in this place) is preferred not only to me or my youth, but even to the truth. And so, I could not refrain from inserting some other things into the aforementioned demonstration, out of a sole love of defending the truth (which ought to be dear to everyone). I am certainly reluctant to descend to this, since it is not difficult to see from afar, as if from a high watchtower, that there will be no lack of those who will accuse me as if I, with a malevolent spirit, wish to carp at and oppose the writings of others, whom indeed I ought to acknowledge as my teachers on account of their age. Since, therefore, I was long deliberating with myself in doubt, finally it occurred to my mind how shameful it is, on account of private calumnies, which are not to be feared from good men, to suffer that violence and injury be inflicted upon the truth. Wherefore, candid reader, I hope that you will be favorable to me in this matter, and indeed that you will agree with me in this on account of your candor, along with the suffrages of all good men, that it is not a sin for me, who, for the search and defense of truth, am accustomed to examine all things (especially mathematical) to the norm of truth, and I do not value anyone's authority more than the demonstrations or proofs of the same author, lest I be deceived by that and wander from these. In this same way, excellent reader, I submit and subject these my present works to your integrity and prudent censure, along with all others which, if the fates grant life, I am to publish in the future, so that you may test and apply them to the said standard.

Most people place this Comet in the air.

Whatever writings I have encountered that have been published about this Comet, most of them wish it to be elemental, not ethereal. Of these, some produce no proofs of their opinion, other than that they do not doubt that the opinion of Aristotle, having been held as true for many centuries, ought not or cannot be called into question by anyone; nor has it crossed their minds that the matter might be otherwise here, whence they say that those who state the contrary should be rejected, since Aristotle's authority is greater than any proof. Others, however, try to defend their opinion a little more subtly, while they descend to Geometric demonstrations from observations which they believe they have seized upon as most true. But I have an answer ready for these.

I judge that those former ones are not unworthy of pardon, since they do not