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 bad 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 Lomomnosoff.193 However, much more than half a century elapsed before the theory appeared 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 as brought again to the front; and we all remember how Darwin’s ideas were carried on and forced on the attention of 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.