the men of his time,—the faculty, namely, of discerning the lines of inquiry in a mass of as yet unrelated facts. He somewhere says that he had found it harder, perhaps, to put the question than it was to reach the answer. This power is the great economizer of mental energy, in any branch of investigation; it is, to the man who has it, equivalent to a compass; and to Darwin it was the one talent without which his stores of knowledge would have been no more than a heap of unclassified specimens in a museum cellar. Moral and physical qualities he had, besides; his patience and his practiced vision were invaluable; but it was the intellectual part that penetrated the secrets of nature. This sense of the problem, this eye for the question, was most serviceable to his success. His acuteness in perceiving the importance of the infinitely little, which is often mentioned as one of his distinguishing traits, was only an incident of this larger endowment; and his power to make other men useful to him, specialists in horticulture or physiology, or even common observing men, was only the knowledge of how to put practical questions. The point is worth emphasizing, because in this age of the accu-
