is something analogous to heaven, the instrument of heaven.” In denying that a spirit descends and stows itself in the body, as “an extraneous inmate,” Harvey advances beyond Cremoninus, who then taught in the chair of Averroistic philosophy in Padua; for, says Harvey, I cannot discover this spirit with my senses, nor any seat of it. In another passage indeed Harvey warns us “not to derive from the stars what is in truth produced at home”; in yet another he tells us that philosophers produce principles as indifferent poets thrust gods upon the stage, to unravel plots and to bring about catastrophes: yet he concludes that “the spirit in the blood acting superiorly to the powers of the elements, ... the soul in this spirit and blood, is identical with the essence of the stars.” Thus the riddle which oppressed these great thinkers, from the Ionians to Lavoisier, was in part the nature of the “impetum faciens[31]”—of the Bildungstrieb. What makes the ball to roll? Does heart move blood or blood move heart; and in either case what builds the organ and what bestows and perpetuates the motion? Albert of Cologne, and at times even Aristotle, as we have seen, were apt to leave moving things for abstract motion, and to regard formulas as agents. Telesius again, the first of the brilliant band of natural philosophers in Italy of the XVIth and XVIIth centuries, was still seeking this principle of nature in the “form” of the peripatetics. Gilbert regarded his magnetic force as “of the nature of soul, surpassing the soul of man.” Galileo, although willing to conceive circular motion as perpetual[32], and even self-existent, was unable thus to conceive rectilineal motion.