xii
Princeton
University Press,
for
lending
her
great
experience
and devotion
to the
finalization of the
present
volume.
Michael Perlman deserves
more
than the usual credit
for
the
preparation
of
the camera-ready
text
and,
especially,
for
the
setting
of Einstein's
numerous
and
frequently
intricate formulas.
A.
Engel, Translator E. L.
Schucking, Consultant