Subjects of investigation so rich and manifold as these may well attract all the most varied gifts of the human mind. This they have already done, and there is every indication that they will continue to do so for generations yet to be. Already an immense literature is devoted to them; and every fresh effort of observation and of reasoning seems to open out new and fruitful avenues of thought. The work which is here introduced to the English reader contains an excellent review of this literature, so far as it is represented in the English and German languages. Knowing the author personally, as I have done for many years, I recognize with pleasure in his work all the carefulness of inquiry, and all the conscientiousness of reasoning, which belong to a singularly candid and patient mind. ARGYLL. INVERARY CASTLE, SCOTLAND, _September, 1882._ * * * * * {7} NOTE BY THE TRANSLATOR. The consideration which this work has received from the leaders of religious and philosophic thought in Germany, and, indeed, wherever it has been read in its original form, has led the translator to believe that an English version of it would be acceptable. Especially in America, where religious problems and religious thought are so intimately connected with the processes of scientific and philosophic investigation, and where the agitation of these problems is so peculiarly active and violent, it has seemed that a work marked by so much scholarship, profundity, and comprehensiveness and originality of treatment, must serve an important purpose to the cause of religious no less than of scientific truth. It may be explained here, that the author resided for some years in the family of the Duke of Argyll, and there breathed, to a certain extent, the scientific air of Darwinism in its very origin; and thus his familiarity with all the results of modern scientific research, added to his theological and philosophical acquirements, enable him, with a most admirable blending of the spirit of fairness and toleration with logical severity of treatment, to bring these different domains into their proper relation with each other and to establish between them that essential harmony in which consists the solution of these most profound and vital problems of man's welfare.