272 RELATIVITY, THE GENERAL THEORYalso thoroughly indigestible.' Shortly afterward, Lorentz once again wrote to
Ehrenfest. 'I had written to Einstein that, now that he has reached the acme of
his theory, it would be important to give an expose of its principles in as simple
a form as possible, so that every physicist (or anyway many of them) may famil-
iarize himself with its content. I added that I myself would very much like to try
doing this but that it would be more beautiful if he did it himself [L4].
Lorentz's fatherly advice must have been one of the incentives that led Einstein
to write his first synopsis of the new theory [E6].* This beautiful, fifty-page
account was completed in March 1916. It was well received. This may have
encouraged Einstein—who did not communicate all that badly—to do more writ-
ing. In December 1916 he completed Uber die spezielle und die allgemeine Rela-
livitdtstheorie, gemeinverstdndlich,** his most widely known work [E8a].
Demand for it became especially high after the results of the eclipse expedition
caused such an immense stir (see Chapter 16). Its tenth printing came out in 1920,
the twenty-second in 1972.
Einstein's paper of March 1916 concludes with a brief section on the three new
predictions: the red shift, the bending of light, and the precession of the perihelion
of Mercury. In the final paragraph of that section is recorded the single major
experimental confirmation which at that time could be claimed for the theory: the
Mercury anomaly. In 1916 next to nothing was known about the red shift; the
bending of light was first observed in 1919.
Commenting on the status of experimental relativity in 1979, David Wilkinson
remarked:
[These] two early successes [—the perihelion precession and the bending of
light—were] followed by decades of painfully slow experimental progress. It
has taken nearly sixty years finally to achieve empirical tests of general relativ-
ity at the one per cent level. Progress... required development of technology
and experimental techniques well beyond those available in the early 1920s.
[W7]I refer the reader to Wilkinson's paper for further remarks on the technological
and sociological aspects of modern relativity experiments. For a summary of the
present status of the experimental verification of general relativity (excluding cos-
mology), the reader should consult the report by Irwin Shapiro wherein it will be
found that, within the errors, all is well with the red shift (both astronomically
and terrestrially), with the bending of light, with the precession of the perihelia
of Mercury and other bodies, and also with the modern refined tests of the equiv-
*This article was published both in the Annalen der Physik and, also in 1916, as a separate booklet
[E7] which went through numerous printings and was also translated into English [E8].
** On the Special and the General Relativity Theory, a Popular Exposition. Under this title, the
English translation appeared in 1920 (Methuen, London). Einstein used to joke that the book should
rather be called 'gemeinunverstandlich,' commonly ununderstandable.