"Kepler in the first thirty years of the seventeenth century "reduced to order the chaos of data" left by , and added to them just the thing that was needed—mathematical genius. Like Copernicus he created another world-system which, since it did not ultimately prevail, merely remains as a strange monument of colossal intellectual power working on insufficient materials; and even more than Copernicus he was driven by semi-religious fervour—a passion to uncover the magic of mere numbers and to demonstrate the music of the spheres. ...He has to his credit a collection of discoveries and conclusions—some of them more ingenious than useful—from which we today can pick out three that have a permanent importance in the history of astronomy."