The interest with which he followed the later development of social problems need not be dwelt on here, except to say that he watched their earlier maturity in America as an indication of the problems which would afterwards call for a solution in his own country. His share in treating them was limited to examining the principles of social philosophy on which some of the proposed remedies for social troubles were based, and this examination may be found in his "Collected Essays." But the educational campaign which he carried on in England had its counterpart in America. It was not only that he was chosen to open the Johns Hopkins University as the type of a new form of education; there and elsewhere pupils of his carried out in America his methods of teaching biology, while others engaged in general education would write testifying to the influence of his ideas upon their own methods of teaching. But it must be remembered that nothing was further from his mind than the desire to found a school of thought. He only endeavoured as a scholar and a student to clear up his own thoughts and help others to clear theirs, whether in the intellectual or the moral world. This was the help he steadfastly hoped to give the people, that interacting union of intellectual freedom and moral discernment which may be furthered by good education and training, by precept and example, that basis of all social health and prosperity. And if, as he said, he would like to be remembered as one who had done his best to help the people, he meant assuredly not the people only of his native land, but the wider world to whom his words could be carried. PREFACE TO THE ENGLISH EDITION. My father's life was one of so many interests, and his work was at all times so diversified, that to follow each thread separately, as if he had been engaged on that alone for a time, would be to give a false impression of his activity and the peculiar character of his labours. All through his active career he was equally busy with research into nature, with studies in philosophy, with teaching and administrative work. The real measure of his energy can only be found when all these are considered together. Without this there can be no conception of the limitations imposed upon him in his chosen life's work. The mere amount of his research is greatly magnified by the smallness of the time allowed for it. But great as was the impression left by these researches in purely scientific circles, it is not by them alone that he made his impression upon the mass of his contemporaries. They were chiefly moved by something over and above his wide knowledge in so many fields--by his passionate sincerity, his interest not only in pure knowledge, but in human life, by his belief that the interpretation of the book of nature was not to be kept apart from the ultimate problems of existence; by the love of truth, in short, both theoretical and practical, which gave the key to the character of the man himself.