The great achievements of the Renaissance were the discovery of the world and the discovery of man.[1] Under these two formulae may be classified all the phenomena which properly belong to this period. The discovery of the world divides itself into two branches--the exploration of the globe, and that systematic exploration of the universe which is in fact what we call Science. Columbus made known America in 1492; the Portuguese rounded the Cape in 1497; Copernicus explained the solar system in 1507. It is not necessary to add anything to this plain statement; for, in contact with facts of such momentous import, to avoid what seems like commonplace reflection would be difficult. Yet it is only when we contrast the ten centuries which preceded these dates with the four centuries which have ensued, that we can estimate the magnitude of that Renaissance movement by means of which a new hemisphere has been added to civilization. In like manner, it is worth while to pause a moment and consider what is implied in the substitution of the Copernican for the Ptolemaic system. The world, regarded in old times as the center of all things, the apple of God's eye, for the sake of which were created sun and moon and stars, suddenly was found to be one of the many balls that roll round a giant sphere of light and heat, which is itself but one among innumerable suns attended each by a _cortege_ of planets, and scattered, how we know not, through infinity. What has become of that brazen seat of the old gods, that Paradise to which an ascending Deity might be caught up through clouds, and hidden for a moment from the eyes of his disciples. The demonstration of the simplest truths of astronomy destroyed at a blow the legends that were most significant to the early Christians by annihilating their symbolism. Well might the Church persecute Galileo for his proof of the world's mobility. Instinctively she perceived that in this one proposition was involved the principle of hostility to her most cherished conceptions, to the very core of her mythology. Science was born, and the warfare between scientific positivism and religious metaphysic was declared. Henceforth God could not be worshiped under the forms and idols of a sacerdotal fancy; a new meaning had been given to the words: 'God is a Spirit, and they that worship Him must worship Him in spirit and in truth.' The reason of man was at last able to study the scheme of the universe, of which he is a part, and to ascertain the actual laws by which it is governed. Three centuries and a half have elapsed since Copernicus revolutionized astronomy. It is only by reflecting on the mass of knowledge we have since acquired, knowledge not only infinitely curious but also incalculably useful in its application to the arts of life, and then considering how much ground of this kind was acquired in the ten centuries which preceded the Renaissance, that we are at all able to estimate the expansive force