If this _X_ force exists and can be established, it will give us the clue, I believe, to much more than the operations of physical nature. The following pages are an attempt to establish it, to define its character, and to indicate the lines on which this unknown factor in evolution seems to bring into a rational unity the phenomena of the physical world and the moral and æsthetic faculties of man. The time appears to have come for such an attempt. The fermentation of mind produced by Darwin’s massive and victorious promulgation of the evolution theory is beginning to subside; it is now possible in some measure to take stock of what has been destroyed, of what has been left intact, by the immense tidal wave of new thought which then swept over the world. Some conceptions which were thought to have been submerged for ever are reappearing in more or less altered shapes, and science is called on to reconstruct a universe less one-sided, less aridly simple, than that which Darwinism, as at first understood, appeared to have left us. The result, so far as it is successful, will be the establishment of a spiritual view of the universe on a natural basis. It is an attempt which is at present occupying many minds, and which will doubtless have to occupy many more before complete success is attained. I propose, in the following pages, to take the reader over the most material and significant part of the ground by which I have myself travelled towards certain conclusions. Much of this ground lies in the region of biological science. No doubt to readers acquainted with that science I shall often seem to delay too long in well-trodden and familiar paths. But I have had to consider the fact that English education is still very much specialized. It is either literary or it is scientific. In the great majority of cases it is literary. And though scientific problems and theories are understood by every educated man and woman to be of deep importance and interest, and though questions like those discussed in the present work are questions on which all such persons are well entitled, and many feel themselves bound, to have an opinion, very few, comparatively, have even the elementary knowledge of science and its terminology necessary to enable them to take up the discussion at an advanced point. When it is announced from time to time that some chemist has again succeeded in forming an organic compound out of inorganic chemical constituents in his laboratory,[3] how many readers are there out of the small circle of trained chemists who would not be far more impressed if they heard that he had made a diamond? It is for these persons—the layman and the lay-woman in point of science—that I mainly write, and my own training having been philosophical and literary rather than scientific I think I understand most of their difficulties. I have, therefore, tried to ‘begin at the beginning’; and I hope that this book, besides