As in effect I dare say, That the exact observation of those few precepts I had chosen, gave me such a facility to resolve all the questions whereto these two sciences extend; That in two or three months space which I employed in the examination of them, having begun by the most simple and most generall, and every Truth which I found being a rule which afterwards served me to discover others; I did not only compasse divers truths which I had formerly judged most difficult, But me thought also that towards the end I could determin even in those which I was ignorant of, by what means and how farr it was possible to resolve them. Wherein perhaps I shall not appear to be very vain if you consider, That there being but one truth of every thing, who ever finds it, knows as much of it as one can know; And that for example a child instructed in Arithmatick having made an addition according to his rules, may be sure to have found, touching the sum he examined, all what the wit of man could finde out. In a word the method which teacheth to folow a right order, and exactly to enumerate all the circumstances of what we seek, contains, whatsoever ascertains the rules of Arithmatick. But that which pleas'd me most in this Method was the assurance I had, wholly to use my reason, if not perfectly, at least as much as it was in my power; Besides this, I perceived in the practice of it, my minde by little and little accustom'd it self to conceive its objects more clearly and distinctly; and having not subjected it to any particular matter, I promised my self to apply it also as profitable to the difficulties, of other sciences as I had to Algebra: Not that I therefore durst at first undertake to examine all which might present themselves, for that were contrary to the order it prescribes. But having observ'd that all their principles were to be borrowed from Philosophy, in which I had yet found none that were certain, I thought it were needfull for me in the first place to endevor to establish some, and that this being the most important thing in the world, wherein precipitation and prevention were the most to be feared, I should not undertake to performe it, till I had attain'd to a riper Age then XXIII. which was then mine. Before I had formerly employed a long time in preparing my self thereunto, aswel in rooting out of my minde all the ill opinions I had before that time received, as in getting a stock of experience to serve afterwards for the subject of my reasonings, and in exercising my self always in the Method I had prescribed. That I might the more and more confine my self therein. PART. III.