This preoccupation with natural phenomena and this refusal to accept the old, established theories until they had been verified by an investigation of common fact was a very novel thing. It introduced a fresh and momentous element into our intellectual heritage. We have recalled the mysticism, supernaturalism, and intolerance of the Middle Ages, their reliance on old books, and their indifference to everyday fact except as a sort of allegory for the edification of the Christian pilgrim. In the mediaeval universities the professors, or "schoolmen", devoted themselves to the elaborate formulation of Christian doctrine and the interpretation of Aristotle's works. It was a period of revived Greek metaphysics, adapted to prevailing religious presuppositions. Into this fettered world Bacon, Galileo, Descartes, and others brought a new aspiration to promote investigation and honest, critical thinking about everyday things. _These founders of modern natural science realized that they would have to begin afresh. This was a bold resolve, but not so bold as must be that of the student of mankind to-day if he expects to free himself from the trammels of the past_. Bacon pointed out that the old days were not those of mature knowledge, but of youthful human ignorance. "_These_ times are the ancient times, when the world is ancient, and not those we count ancient, _ordine retrogrado_, by a computation backward from ourselves." In his _New Atlantis_ he pictures an ideal State which concentrated its resources on systematic scientific research, with a view to applying new discoveries to the betterment of man's lot. Descartes, who was a young man when Bacon was an old one, insisted on the necessity, if we proposed to seek the truth, of questioning _everything_ at least once in our lives. To all these leaders in the development of modern science doubt, not faith, was the beginning of wisdom. They doubted--and with good reason--what the Greeks were supposed to have discovered; they doubted all the old books and all the university professors' lecture notes. They did not venture to doubt the Bible, but they eluded it in various ways. They set to work to find out exactly what happened under certain circumstances. They experimented individually and reported their discoveries to the scientific academies which began to come into existence.