194 RELATIVITY, THE GENERAL THEORYlib. 1911. The Bending of Light is Detectable
Do not Bodies act upon Light at a distance, and by their action
bend its Rays; and is not this action (caeteris paribus) strongest
at the least distance?
ISAAC NEWTON: Opticks, Query 1Einstein finally broke his silence about gravitation in June 1911 [E8]. He had
become dissatisfied with his presentation of 1907 [E9]. 'More than that, I now
realize that one of the most important consequences of those considerations is ame-
nable to experimental verification.' This is the bending of light. He had already
been aware of this phenomenon in 1907. However, at that time he had thought
only of terrestrial experiments as a means of its observation and had concluded
that these would be too hard to perform (still true to this day). Meanwhile it had
dawned on him that deflection of light by the sun could be detectable. He also had
other new conclusions to report.
The resulting paper, 'On the Influence of Gravitation on the Propagation of
Light,' is included in Das Relativitatsprinzip, which first appeared in 1913, a
handy little book (English translation, [LI]). Its later editions contain contribu-
tions to relativity theory by Lorentz, Minkowski, Einstein, and Weyl. The book
has two flaws. First, there is no contribution by Poincare. Poincare's memoir of
1905 is lengthy and does not readily fit into this small volume. However, a frag-
ment could easily have been included, especially since one of Lorentz's papers does
appear in abridged form. A second shortcoming of the book is the absence of the
brief Section V of Einstein's 1907 article [E9]. Either this piece should have been
included along with his 1911 article or else both should have been omitted, since
the finer points of the 1911 paper cannot be understood without the approxima-
tions he had used in 1907.
In the 1911 paper Einstein cautioned his readers, 'Even if the theoretical foun-
dation is correct, the relations derived here are valid only in first approximation,'
but did not add an explicit statement about the nature of this approximation. He
had yet to acquire the skill of reiterating conclusions from his own earlier work.
This is not surprising. Prior to Einstein's involvement with gravitation, each
one of his papers is transparent and self-contained (with the possible exception of
his earliest writing on the foundations of statistical mechanics) though his readers
may occasionally have to go to some effort to realize that. We have seen on various
earlier occasions that Einstein did not go to great trouble to search the literature
for contributions by others, but that was no particular hindrance to an understand-
ing of what he himself had to communicate. Of course, he would return now and
then to a subject he had discussed earlier, but then the new contribution would
again be self-contained. We know that sometimes he had thought long and hard
before gaining a new insight, as in the case of special relativity. Yet little if any
sign of the preceding struggle is found in the resulting papers, which rather give
the impression of a man hugely enjoying himself. From 1907 until 1916, this light