"Out of the pictures which are all that we can really see, we imagine a world of solid things; and... this world is constructed so as to fullfil a certain code of rules, some called axioms, and some called definitions, and some called postulates, and some assumed in the course of demonstration, but all laid down in one form or another in Euclid’s Elements of Geometry. ...This book has been for nearly twenty-two centuries the encouragement and guide of that scientific thought which is one... with the progress of man from a worse to a better state. The encouragement; for it contained a body of knowledge that was really known and could be relied on, and that moreover was growing in extent and application. For even at the time this book was written—shortly after the foundation of the Alexandrian Museum—Mathematic was no longer the merely ideal science of the Platonic school, but had started on her career of conquest over the whole world of Phenomena. The guide; for the aim of every scientific student of every subject was to bring his knowledge of that subject into a form as perfect as that which geometry had attained. Far up on the great mountain of Truth, which all the sciences hope to scale, the foremost of that sacred sisterhood was seen, beckoning for the rest to follow her. And hence she was called, in the dialect of the Pythagoreans, “the purifier of the reasonable soul.” Being thus in itself at once the inspiration and the aspiration of scientific thought, this book of Euclid has had a history as chequered as that of human progress itself."