I own two mementos of Einstein, which I cherish. One is his last pipe. Its head
is made of clay, its stem is a reed. Helen Dukas presented it to me some time in
- The other is the galley proof of Appendix II, 'Generalized Theory of Grav-
itation,' which appeared first in the 1950 edition of his The Meaning of Relativity.
On the opening page of the proofs, the following words are written in a slightly
shaky hand: Tauli: nach Einsichtnahme bitte Pais geben. A. E.,' P.: after perusal
please give to P. I was in my thirties when that 1950 book came out. I read it then
and have reread it once every few years, always with the same thought as I turn
the pages. Does the man never stop?
Now I react similarly to the Jahrbuch article, which I first read at a later age.
This review does not have the perfection of the 1905 paper on special relativity.
The approximations are clumsy and mask the generality of the conclusions. Ein-
stein was the first to say so, in 1911. The conclusion about the bending of light is
qualitatively correct, quantitatively wrong—though, in 1907, not yet logically
wrong. Einstein was the first to realize this, in 1915. Despite all that, I admire
In a gravitational field, one must associate with every energy E an additional
position-dependent energy which equals the position-dependent energy of a "pon-
derable" mass of magnitude E/c^2. The law [ E = me^2 ] ... therefore holds not
only for inertial but also for gravitational mass.'
As said, the Jahrbuch article was received by the editor on December 4. On
December 24, Einstein wrote to Conrad Habicht:
At this time I am [again] busy with considerations on relativity theory in con-
nection with the law of gravitation.... I hope to clear up the so-far unexplained
secular changes of the perihelion length of Mercury... [but] so far it does not
seem to work. [E8]
l82 RELATIVITY, THE GENERAL THEORYdescription in S with the one in E, using the local inertial frame S' as an inter-
mediary. The steps are straightforward. I omit the details and state only his
results.
Einstein finds, first, that the Maxwell equations in E have the same form as in
S, but with the velocity of light c in S replaced by:in E. 'It follows from this that the light rays which do not run in the £ direction
are bent by the gravitational field.' Second, he examines the energy conservation
law in E and finds 'a very notable result. An energy E [defined as an energy for
the case of no gravitational field] ... contributes to the total energy an additional
position dependent amount