it to be impossible in Nature, as to your _Author_ it seems, That _Water should not be transchangeable into Air_; for, that he says, _The Air would have increased into a huge bulk, and all Water would have long since failed_: It is no consequence, because there is a Mutual transmutation of all figures and parts of Nature, as I declared above; and when one part is transchanged into another, that part is supplied again by the change of another, so that there can be no total mutation of kinds or sorts of figures, but onely a mutual change of the particulars. Neither is it of any consequence, when your _Author_ says, That _if Water should once be turned into Air, it would always remain Air, because a returning agent is wanting, which may turn Air again into Water._ For he might as well say, a Man cannot go or turn backward, being once gone forward. And although he brings a General Rule, That _every thing, as much as in it lies, doth desire to remain in it self_; Yet it is impossible to be done, by reason there is no rest in Nature, she being in a perpetual motion, either working to the consistance of a figure, or to the uniting of several parts, or to the dissolving or dividing of several parts, or any other ways. By dissolving, I do not mean annihilating, but such a dissolving of parts as is proper for the altering of such a figure into one or many other figures. But rather then your Author will consent to the transchanging of Water into Air, he will feign several grounds, soils or pavements in the Air, which he calls _Peroledes_, and so many Flood-gates and Folding-dores, and make the Planets their Key-keepers; which are pretty Fancies, but not able to prove any thing in Natural Philosophy. And so leaving them to their Author, I rest, Madam, _Your humble and_ _faithful Servant._ [1] _Ch._ Of the Gas of Water. V. _MADAM,_