RIGHT HONORABLE, MY MOST HONORED LORD, WILLIAM, EARL OF DEVONSHIRE. ------- This first section of the Elements of Philosophy, the monument of my service and your Lordship's bounty, though, after the Third Section published, long deferred, yet at last finished, I now present, my most excellent Lord, and dedicate to your Lordship. A little book, but full; and great enough, if men count well for great; and to an attentive reader versed in the demonstrations of mathematicians, that is, to your Lordship, clear and easy to understand, and almost new throughout, without any offensive novelty. I know that that part of philosophy, wherein are considered lines and figures, has been delivered to us notably improved by the ancients; and withal a most perfect pattern of the logic by which they were enabled to find out and demonstrate such excellent theorems as they have done. I know also that the hypothesis of the earth's diurnal motion was the invention of the ancients; but that both it, and astronomy, that is, celestial physics, springing up together with it, were by succeeding philosophers strangled with the snares of words. And therefore the beginning of astronomy, except observations, I think is not to be derived from farther time than from Nicolaus Copernicus; who in the age next preceding the present revived the opinion of Pythagoras, Aristarchus, and Philolaus. After him, the doctrine of the motion of the earth being now received, and a difficult question thereupon arising concerning the descent of heavy bodies, Galileus in our time, striving with that difficulty, was the first that opened to us the gate of natural philosophy universal, which is the knowledge of the nature of _motion_. So that neither can the age of natural philosophy be reckoned higher than to him. Lastly, the science of _man's body_, the most profitable part of natural science, was first discovered with admirable sagacity by our countryman Doctor Harvey, principal Physician to King James and King Charles, in his books of the _Motion of the Blood_, and of the _Generation of Living Creatures_; who is the only man I know, that conquering envy, hath established a new doctrine in his life-time. Before these, there was nothing certain in natural philosophy but every man's experiments to himself, and the natural histories, if they may be called certain, that are no certainer than civil histories. But since these, astronomy and natural philosophy in general have, for so little time, been extraordinarily advanced by Joannes Keplerus, Petrus Gassendus, and Marinus Mersennus; and the science of human bodies in special by the wit and industry of physicians, the only true natural philosophers, especially of our most learned men of the College of Physicians in London. Natural Philosophy is therefore but young; but Civil Philosophy yet much younger, as being