that being curiously adapted into one Systeme, they need not each of them any other defence then that which their mutuall Coherence gives them: As 'tis in an Arch, where each single stone, which if sever'd from the rest would be perhaps defenceless, is sufficiently secur'd by the solidity and entireness of the whole Fabrick of which it is a part. How justly this may be apply'd to the present case, I could easily shew You, if I were permitted to declare to You, how harmonious _Aristotles_ Doctrine of the Elements is with his other Principles of Philosophy; and how rationally he has deduc'd their number from that of the combinations of the four first Qualities from the kinds of simple Motion belonging to simple bodies, and from I know not how many other Principles and _Phaenomena_ of Nature, which so conspire with his Doctrine of the Elements, that they mutually strengthen and support each other. But since 'tis forbidden me to insist on Reflections of this kind, I must proceed to tell You, that though the Assertors of the four Elements value Reason so highly, and are furnish'd with Arguments enough drawn from thence, to be satisfi'd that there must be four Elements, though no Man had ever yet made any sensible tryal to discover their Number, yet they are not destitute of Experience to satisfie others that are wont to be more sway'd by their senses then their Reason. And I shall proceed to consider the testimony of Experience, when I shall have first advertis'd You, that if Men were as perfectly rational as 'tis to be wish'd they were, this sensible way of Probation would be as needless as 'tis wont to be imperfect. For it is much more high and Philosophical to discover things _a priore_, then _a posteriore_. And therefore the Peripateticks have not been very sollicitous to gather Experiments to prove their Doctrines, contenting themselves with a few only, to satisfie those that are not capable of a Nobler Conviction. And indeed they employ Experiments rather to illustrate then to demonstrate their Doctrines, as Astronomers use Sphaeres of pastboard, to descend to the capacities of such as must be taught by their senses, for want of being arriv'd to a clear apprehension of purely Mathematical Notions and Truths. I speak thus _Eleutherius_ (adds _Themistius_) only to do right to Reason, and not out of Diffidence of the Experimental proof I am to alledge. For though I shall name but one, yet it is such a one as will make all other appear as needless as it self will be found Satisfactory. For if You but consider a piece of green-Wood burning in a Chimney, You will readily discern in the disbanded parts of it the four Elements, of which we teach It and other mixt bodies to be compos'd. The fire discovers it self in the flame by its own light; the smoke by ascending to the top of the chimney, and there readily vanishing into air, like a River losing it self in the Sea, sufficiently manifests to what Element it belongs and gladly returnes.