  This note is devoted to a detail concerning the work of Albert Einstein and
Peter Bergmann on unified theories of electromagnetism and gravitation in five
dimensions. In their paper of 1938, Einstein and Bergmann were among the first
to introduce the modern viewpoint in which a four-dimensional theory that
coincides with Einstein-Maxwell theory at long distances is derived from a
five-dimensional theory with complete symmetry among all five dimensions. But
then they drew back, modifying the theory in a way that spoiled the
five-dimensional symmetry and looks contrived to modern readers. Why? According
to correspondence of Peter Bergmann with the author, the reason was that the
more symmetric version of the theory predicts the existence of a new long range
field (a massless scalar field). In 1938, Einstein and Bergmann did not wish to
make this prediction. (Based on a lecture at the Einstein Centennial
Celebration at the Library of Alexandria, June, 2005.
