France and of reporting upon the state of the studies there
pursued. Hence he is in an excellent position to appreciate at
its proper value the extraordinary change which has lately
revolutionized physical science, while his official position has
kept him aloof from the controversies aroused by the discovery of
radium and by recent speculations on the constitution of matter.

M. Poincaré's object and method in writing the book are
sufficiently explained in the preface which follows; but it may
be remarked that the best of methods has its defects, and the
excessive condensation which has alone made it possible to
include the last decade's discoveries in physical science within
a compass of some 300 pages has, perhaps, made the facts here
noted assimilable with difficulty by the untrained reader. To
remedy this as far as possible, I have prefixed to the present
translation a table of contents so extended as to form a fairly
complete digest of the book, while full indexes of authors and
subjects have also been added. The few notes necessary either for
better elucidation of the terms employed, or for giving account
of discoveries made while these pages were passing through the
press, may be distinguished from the author's own by the
signature "ED."

THE EDITOR.

ROYAL INSTITUTION OF GREAT BRITAIN,
April 1907.