So much for the past history of mankind, during which many things conspired to make progress in the subjugation of nature slow, fitful, and fortuitous. What of the future? Bacon's answer is: if the errors of the past are understood and avoided there is every hope of steady progress in the modern age. But it might be asked. Is there not something in the constitution of things which determines epochs of stagnation and vigour, some force against which man's understanding and will are impotent? Is it not true that in the revolutions of ages there are floods and ebbs of the sciences, which flourish now and then decline, and that when they have reached a certain point they can proceed no further? This doctrine of Returns or ricorsi [Footnote: Bodin's conversiones.] is denounced by Bacon as the greatest obstacle to the advancement of knowledge, creating, as it does, diffidence or despair. He does not formally refute it, but he marshals the reasons for an optimistic view, and these reasons supply the disproof The facts on which the fatalistic doctrine of Returns is based can be explained without resorting to any mysterious law. [Footnote: Nov. Org. i. 92 sqq.] Progress has not been steady or continuous on account of the prejudices and errors which hindered men from setting to work in the right way. The difficulties in advancing did not arise from things which are not in our power; they were due to the human understanding, which wasted time and labour on improper objects. "In proportion as the errors which have been committed impeded the past, so do they afford reason to hope for the future." 4. But will the new period of advance, which Bacon expected and strove to secure, be of indefinite duration? He does not consider the question. His view that he lived in the old age of the world implies that he did not anticipate a vast tract of time before the end of mankind's career on earth. And an orthodox Christian of that time could hardly be expected to predict. The impression we get is that, in his sanguine enthusiasm, he imagined that a "prudent interrogation" of nature could extort all her secrets in a few generations. As a reformer he was so engaged in the immediate prospect of results that his imagination did not turn to the possibilities of a remoter future, though these would logically follow from his recognition of "the inseparable propriety of time which is ever more and more to disclose truth." He hopes everything from his own age in which learning has made her third visitation to the world, a period which he is persuaded will far surpass that of Grecian and Roman learning. [Footnote: Advancement, ii. 24.] If he could have revisited England in 1700 and surveyed what science had performed since his death his hopes might have been more than satisfied.