It was the same with physics. The physics of the ancients were heaps of conjecture. The predecessors of Galileo abandoned conjecture, put themselves face to face with Nature, observed and classified phenomena, but possessed no method by which their labors could be made productive of cumulative results. But after Galileo had experimented with balls of a given weight on an inclined plane, and Torricelli had pushed upward a weight equal to a known column of water, and Stahl had reduced metals to lime and transformed lime back again into metal, by the addition and subtraction of certain parts, the naturalists carried a torch that illumined their path. They perceived that reason lays her own plans, takes the initiative with her own principles, and must compel nature to answer her questions, instead of obsequiously following its leading-string. It was discovered that scattered observations, made in obedience to no fixed plan, and associated with no necessary law, could not be brought into systematic form. The discovery of such a law is a necessity of reason. Reason presents herself before nature, holding in one hand the principles which alone have power to bring into order and harmony the phenomena of nature; in the other hand grasping the results of experiment conducted according to those principles. Reason demands knowledge of nature, not as a docile pupil who receives implicitly the master's word, but as a judge who constrains witnesses to reply to questions put to them by the court. To this attitude are due the happy achievements in physics; reason seeking--not fancying--in nature, by conformity with her own rules, what nature ought to teach, and what of herself she could not learn. Thus physics became established upon the solid basis of a science, after centuries of error and groping. Wherefore now, asks Kant, are metaphysics so far behind logic, mathematics, and physics? Wherefore these heaps of conjecture, these vain attempts at solution? Wherefore these futile lives of great men, these abortive flights of genius? The study of the mind is not an arbitrary pursuit, suggested by vanity and conducted by caprice, to be taken up idly and relinquished at a moment's notice. The human mind cannot acquiesce in a judgment that condemns it to barrenness and indifference in respect to such questions as God, the Soul, the World, the Life to Come; it is perpetually revising and reversing the decrees pronounced against itself. It must accept the conditions of its being.