Are they not the weeds that prevent the corn coming up, so that they may cover all the ground themselves? And then there happens that which has been well and freshly described by the lamented Feuchtersleben,[1] who died so young: how people cry out in their haste that nothing is being done, while all the while great work is quietly growing to maturity; and then, when it appears, it is not seen or heard in the clamor, but goes its way silently, in modest grief: "_Ist doch"--rufen sie vermessen-- Nichts im Werke, nichts gethan!" Und das Grosse, reift indessen Still heran_. _Es ersheint nun: niemand sieht es, Niemand hört es im Geschrei Mit bescheid'ner Trauer zieht es Still vorbei_. [Footnote 1: _Translator's Note_.--Ernst Freiherr von Feuchtersleben (1806-49), an Austrian physician, philosopher, and poet, and a specialist in medical psychology. The best known of his songs is that beginning "_Es ist bestimmt in Gottes Rath_" to which Mendelssohn composed one of his finest melodies.] This lamentable death of the critical faculty is not less obvious in the case of science, as is shown by the tenacious life of false and disproved theories. If they are once accepted, they may go on bidding defiance to truth for fifty or even a hundred years and more, as stable as an iron pier in the midst of the waves. The Ptolemaic system was still held a century after Copernicus had promulgated his theory. Bacon, Descartes and Locke made their way extremely slowly and only after a long time; as the reader may see by d'Alembert's celebrated Preface to the _Encyclopedia_. Newton was not more successful; and this is sufficiently proved by the bitterness and contempt with which Leibnitz attacked his theory of gravitation in the controversy with Clarke.[1] Although Newton lived for almost forty years after the appearance of the _Principia_, his teaching was, when he died, only to some extent accepted in his own country, whilst outside England he counted scarcely twenty adherents; if we may believe the introductory note to Voltaire's exposition of his theory. It was, indeed, chiefly owing to this treatise of Voltaire's that the system became known in France nearly twenty years after Newton's death. Until then a firm, resolute, and patriotic stand was made by the Cartesian _Vortices_; whilst only forty years previously, this same Cartesian philosophy had been forbidden in the French schools; and now in turn d'Agnesseau, the Chancellor, refused Voltaire the _Imprimatur_ for his treatise on the Newtonian doctrine. On the other hand, in our day Newton's absurd theory of color still completely holds the field, forty years after the publication of Goethe's. Hume, too, was disregarded up to his fiftieth year, though he began very early and wrote in a thoroughly popular style. And Kant, in spite of having written and talked all his life long, did not become a famous man until he was sixty. [Footnote 1: See especially §§ 35, 113, 118, 120, 122, 128.]