Some will say, of course, that to reduce men of science to the _rôle_ of manual workers would mean the decay of science and genius. But those who will take into account the following considerations probably will agree that the result ought to be the reverse--namely, such a revival of science and art, and such a progress in industry, as we only can faintly foresee from what we know about the times of the Renaissance. It has become a commonplace to speak with emphasis about the progress of science during the nineteenth century; and it is evident that our century, if compared with centuries past, has much to be proud of. But, if we take into account that most of the problems which our century has solved already had been indicated, and their solutions foreseen, a hundred years ago, we must admit that the progress was not so rapid as might have been expected, and that something hampered it. The mechanical theory of heat was very well foreseen in the last century by Rumford and Humphry Davy, and even in Russia it was advocated by Lomonosoff.[193] However, much more than half a century elapsed before the theory reappeared in science. Lamarck, and even Linnæus, Geoffroy Saint-Hilaire, Erasmus Darwin, and several others were fully aware of the variability of species; they were opening the way for the construction of biology on the principles of variation; but here, again, half a century was wasted before the variability of species was brought again to the front; and we all remember how Darwin’s ideas were carried on and forced on the attention of university people, chiefly by persons who were not professional scientists themselves; and yet in Darwin’s hands the theory of evolution surely was narrowed, owing to the overwhelming importance given to only one factor of evolution. For many years past astronomy has been needing a careful revision of the Kant and Laplace’s hypothesis; but no theory is yet forthcoming which would compel general acceptance. Geology surely has made wonderful progress in the reconstitution of the palæontological record, but dynamical geology progresses at a despairingly slow rate; while all future progress in the great question as to the laws of distribution of living organisms on the surface of the earth is hampered by the want of knowledge as to the extension of glaciation during the Quaternary epoch.[194] In short, in each branch of science a revision of the current theories as well as new wide generalisations are wanted. And if the revision requires some of that inspiration of genius which moved Galileo and Newton, and which depends in its appearance upon general causes of human development, it requires also an increase in the number of scientific workers. When facts contradictory to current theories become numerous, the theories must be revised (we saw it in Darwin’s case), and thousands of simple intelligent workers in science are required to accumulate the necessary facts.