He thinkes that there are not Comets in the heavens, because there may be many other reasons of such appearances, but what he knowes not, perhaps (he saies) that argument from the parallax is not sufficient, or if it be, then there may be some deceit in the observation. To this I may safely say, that hee may justly be accounted a weake Mathematician who mistrusts the strength of this argument, nor can hee know much in Astronomy, who understands not the parallax, which is the foundation of that Science, and I am sure that hee is a timorous man, who dares not believe the frequent experience of his senses, or trust to a demonstration. [Sidenote 1*: _Epist. 95._] True indeed, I grant tis possible, that the eye, the _medium_, and the distance may al deceive the beholder, but I would have him shew which of all these was likely to cause an error in this observation? Meerely to say they might be deceived is no sufficient answer, for by this I might confute the positions of all Astronomers, and affirme the starres are hard by us, because ’tis possible they may be deceived in their observing that distance. But I forbeare any further reply; my opinion is of that Treatise, that either it was set forth purposely to tempt a confutation, that hee might see the opinion of _Galilæus_ confirmed by others, or else it was invented with as much haste and negligence as it was printed, there being in it almost as many faults as lines. Others thinke that these are not any new Comets, but some ancient starres that were there before, which now shine with that unusuall brightnesse, by reason of the interposition of such vapors which doe multiply their light, and so the alteration will be here onely, and not in the heavens. Thus _Aristotle_ thought the appearance of the milkie way was produced, for he held that there were many little starres, which by their influence did constantly attract such a vapour towards that place of heaven, so that it alwaies appeared white. Now by the same reason may a brighter vapor be the cause of these appearances. But how probable soever this opinion may seeme, yet if well considered, you shall finde it to be altogether absurd and impossible: for, 1. These starres were never seene there before, and tis not likely that a vapour being hard by us can so multiply that light which could not before be at all discerned. 2. This supposed vapour cannot be either contracted into a narrow compasse or dilated into a broad: 1. it could not be within a little space, for then that starre would not appeare with the same multiplied light to those in other climates: 2. it cannot be a dilated vapour, for then other starres which were discerned through the same vapour would seeme as bigg as that; this argument is the same in effect with that of the paralax, as you may see in this Figure. [Illustration]