A PRÆFACE INTRODUCTORY To the following Treatise.

among all the Instances he brings to invalidate all the Vulgar Doctrine of those he Disputes with, any one be Irrefragable, that alone is sufficient to overthrow a Doctrine which Universally asserts what he opposes. For, it cannot be true, that all Bodies whatsoever that are reckon’d among the Perfectly mixt Ones, are Compounded of such a Determinate Number of such or such Ingredients, in case any one such Body can be produc’d, that is not so compounded; and he hopes too, that Accurateness will be the less expected from him, because his undertaking obliges him to maintain such Opinions in Chymistry, and that chiefly by Chymical Arguments, as are Contrary to the very Principles of the Chymists; From whose writings it is not Therefore like he should receive any intentionall Assistance, except from some Passages of the Bold and Ingenious Helmont, with whom he yet disagrees in many things (which reduce him to explicate Divers Chymical Phænomena, according to other Notions;) And of whose Ratiocinations, not only some seem very Extravagant, but even the Rest are not wont to be as considerable as his Experiments. And though it be True indeed, that some Aristotelians have occasionally written against the Chymical