PREFACE TO ORIGINAL EDITION.

The present book has for its object the presentation of the
lectures which I delivered as foreign lecturer at Columbia Uni¬
versity in the spring of the present year under the title : " The
Present System of Theoretical Physics." The points of view
which influenced me in the selection and treatment of the
material are given at the beginning of the first lecture. Essen¬
tially, they represent the extension of a theoretical physical
scheme, the fundamental elements of which I developed in an
address at Leyden entitled: *' The Unity of the Physical Concept
of the Universe." Therefore I regard it as advantageous to
consider again some of the topics of that lecture. The presen¬
tation will not and can not, of course, claim to cover exhaus¬
tively in all directions the principles of theoretical physics.

The Author.

Berlin, 1909.