A revulsion, however, occurred in the century of the Reformation, with the breaking down of the blind belief in authority which had till then prevailed in all provinces of human knowledge and thought. After a long and severe struggle, dry scholasticism was finally overcome, and natural science, with the rest, turned from a mere reliance on books to original thinking and personal observation. Thenceforward interpretations of natural processes were sought for no longer in the writings of the ancients, but in Nature herself. Of the magnitude of this emancipation, and of the severity of the struggle against deep-rooted authority, one could form a faint idea from experience even in my own youth. Our young minds were so deeply imbued with the involuntary feeling that the ancients were superior to us moderns in each and every respect, that not only the hardly re-attainable plastic art of the Greeks and the immortal songs of Homer, but all the mental products of antiquity seemed to us models which could never be equalled; the tragedies of Sophocles were for us the greatest tragedies that the world had ever seen, the odes of Horace the most beautiful poems of all time! In the domain of natural science the new era began with the overthrow of the Ptolemaic cosmogony, which, for more than a thousand years, had served as a basis for astronomy. When the German canon, Nicolas Copernicus (born at Thorn, 1473, died 1543), reversed the old theory, and showed that the sun did not revolve round the earth, but the earth round the sun, the ice was broken and the way paved for further progress. Galilei uttered his famous 'e pur si muove,' Kepler established his three laws of the movements of the planets, and Newton, a century later, interpreted their courses in terms of the law of gravitation. But we have not here to do with a history of physics or astronomy, and I only wish to recall these well-known facts, in order that we may see how increased knowledge in this domain was always accompanied by advances in that of biology. Here, however, we cannot yet chronicle any such thoroughgoing revolution of general conceptions; the basis of detailed empirical knowledge was not nearly broad enough for that, and it was in the acquiring of such a foundation that the next three centuries, from the sixteenth to the end of the eighteenth, were eagerly occupied.