TRANSLATOR'S PREFACE.

At the request of the Adams Fund Advisory Committee, and
with the consent of the author, the following translation of Pro¬
fessor Planck's Columbia Lectures was undertaken. It is hoped
that the translation will be of service to many of those inter¬
ested in the development of theoretical physics who, in spite of
the inevitable loss, prefer a translated text in English to an
original text in German. Since the time of the publication of
the original text, some of the subjects treated, particularly that
of heat radiation, have received much attention, with the result
that some of the points of view taken at that time have under¬
gone considerable modifications. The author considers it de¬
sirable, however, to have the translation conform to the original
text, since the nature and extent of these modifications can
best be appreciated by reference to the recent literature relat¬
ing to the matters in question.

A. P. Wills.