Experiments when they are set down only by way of Prescriptions, and not of Relations; that is, unless he that delivers them mentions his doing it upon his own particular knowledge, or upon the Relation of some credible person, avowing it upon his own experience. For I am troubled, I must complain, that even Eminent Writers, both Physitians and Philosophers, whom I can easily name, if it be requir'd, have of late suffer'd themselves to be so far impos'd upon, as to Publish and Build upon Chymical Experiments, which questionless they never try'd; for if they had, they would, as well as I, have found them not to be true. And indeed it were to be wish'd, that now that those begin to quote Chymical Experiments that are not themselves Acquainted with Chymical Operations, men would Leave off that Indefinite Way of Vouching the Chymists say this, or the Chymists affirme that, and would rather for each Experiment they alledge name the Author or Authors, upon whose credit they relate it; For, by this means they would secure themselves from the suspition of falshood (to which the other Practice Exposes them) and they would Leave the Reader to Judge of what is fit for him to Believe of what is Deliver'd, whilst they employ not their own great names to Countenance doubtfull Relations; and they will also do Justice to the Inventors or Publishers of true Experiments, as well as upon the Obtruders of false ones. Whereas by that general Way of quoting the Chymists, the candid Writer is Defrauded of the particular Praise, and the Impostor escapes the Personal Disgrace that is due to him._ _The remaining Part of this Praeface must be imploy'd in saying something for_ Carneades, _and something for my Self._ _And first_, Carneades _hopes that he will be thought to have disputed civilly and Modestly enough for one that was to play the Antagonist and the Sceptick. And if he any where seem to sleight his Adversaries Tenents and Arguments, he is willing to have it look'd upon as what he was induc'd to, not so much by his Opinion of them, as the Examples of_ Themistius _and_ Philoponus, _and the custom of such kind of Disputes._