of them, neither because they had, or had not been said by others, but only because Reason perswaded me to them. If Mechanicks cannot so soon put in practise the Invention which is set forth in the Opticks, I beleeve that therefore men ought not to condemn it; forasmuch as skill and practice are necessary for the making and compleating the Machines I have described; so that no circumstance should be wanting. I should no less wonder if they should succeed at first triall, then if a man should learn in a day to play excellently well on a Lute, by having an exact piece set before him. And if I write in French, which is the language of my Country, rather then in Latin, which is that of my Tutors, 'tis because I hope such who use their meer naturall reason, wil better judge of my opinions, then those who only beleeve in old Books. And for those who joyn a right understanding with study, (who I only wish for my Judges) I assure my self, they will not be so partiall to the Latin, as to refuse to read my reasons because I expresse them in a vulgar tongue. To conclude, I will not speak here in particular of the progresse I hoped to make hereafter in Learning; Nor engage my self by any promise to the Publick, which I am not certain to perform. But I shall onely say, That I am resolved to employ the remainder of my life in no other thing but the study to acquire some such knowledge of Nature as may furnish us with more certain rules in Physick then we hitherto have had: And that my inclination drives me so strongly from all other kind of designes, chiefly from those which cannot be profitable to any, but by prejudicing others; that if any occasion obliged me to spend my time therein, I should beleeve I should never succeed therein: which I here declare, though I well know it conduceth not to make me considerable in the world; neither is it my ambition to be so. And I shall esteem my self always more obliged to those by whose favour I shal without disturbance enjoy my ease, then to them who should proffer me the most honourable imployment of the earth. FINIS.