AUTHOR'S PREFACE. little book will be found to contain the sub- J- stance and general plan of the two lectures I gave at- Strasburg towards the close of last autumn, and the almost literal reproduction of the article published by me in the Sevue des Deux Mondes of the 1st January, 1870. The occasional alterations that may be remarked are, perhaps, explained by the difference that naturally suggests itself between a discourse, delivered in a Protestant Church, and an article subjected to the conditions of publication imposed by such a periodical as the above, and, again, between this and a pamphlet placed before the public upon the writer's sole authority. These alterations, moreover, affect the-form only of the essay, and a few details ; its basis, and the development of the "ideas, remain unchanged. I would take advantage of this opportunity of thanking my Strasburg hearers for the kind interest of which they have given me so many proofs, and of which the publication of this essay is at once a result and a new mark. A. E. Botterdam, January, 1870.