But though much may be said to Excuse the Chymists when they write Darkly, and Ænigmatically, about the Preparation of their Elixir, and Some few oth… - Robert Boyle

Not that I at all disallow the use of reasoning upon experiments, or the endeavouring to discern as early as we can the confederations, and differences, and tendencies of things: for such an absolute suspension of the exercise of reasoning were exceeding troublesome, if not impossible. And, as in that rule of arithmetic, which is commonly called by proceeding upon a conjecturally-supposed number, as if it were that, which we inquire after, we are wont to come to the knowledge of the true number sought for; so in physiology it is sometimes conducive to the discovery of truth, to permit the understanding to make an hypothesis, in order to the explication of this or that difficulty, that by examining how far the phænomena are, or are not, capable of being solved by that hypothesis, the understanding may, even by its own errors, be instructed.

Since a great part of those Learned Men, especially Physicians who have discerned the defects of the vulgar Philosophy, but are not yet come to understand and relish the Corpuscularian, have slid into the Doctrine of the Chymists; and since the Spagyrists are wont to pretend to make out all the Qualities of bodies from the Predominancy of some one of their three Hypostatical Principles, I suppose it may both keep my opinion from appearing too presumptuous, and (which is far more considerable) may make way for the fairer Reception of the Mechanical Hypothesis about Qualities, if I here intimate (though but briefly and in general) some of those defects, that I have observed in Chymists Explications of Qualities.

And that you may know... what kind of writings I mean, I shall name to you the learned Gassendus his little Syntagma of Epicurus's philosophy, and that most ingenious gentleman Monsieur Descartes his principles of philosophy. For though I purposely refrained, though not altogether from transiently consulting about a few particulars, yet from seriously and orderly reading over those excellent (though disagreeing) books, or so much as Sir Francis Bacon's Novum Organum, that I might not be prepossessed with any theory or principles, till I had spent some time in trying what things themselves would incline me to think; yet beginning now to allow myself to read those excellent books, I find by the little I have read in them already, that if I had read them before I began to write, I might have enriched the ensuing essays with divers truths, which they now want, and have explicated divers things much better than I fear I have done.