This book aims to give an account of some of the leading developments in our knowledge of atomic structure and the
interpretation of spectroscopic and electronic phenomena which have
been made in the past four years. This period has probably been
the most exciting in the history of theoretical physics. About
1923 and 1924 there was a pause in the rapid advances which
occurred in the decade immediately following Bohr's theory of
1913. It seemed that all the advances that could be made with
that patchwork theory had been made, and the difficulties which
it had always involved came more and more to the front.