l68 RELATIVITY, THE SPECIAL THEORYneeds to make still a third hypothesis, much more surprising, much more difficult
to accept, one which is of much hindrance to what we are currently used to. A
body in translational motion suffers a deformation in the direction in which it is
displaced. ... However strange it may appear to us, one must admit that the third
hypothesis is perfectly verified.' It is evident that as late as 1909 Poincare did not
know that the contraction of rods is a consequence of the two Einstein postulates.
Poincare therefore did not understand one of the most basic traits of special
relativity.
Should one give Poincare the benefit of the doubt and assume that his reference
to a third hypothesis was made only for pedagogical reasons? This, I think, would
be too far-fetched. Moreover, if one rereads his earlier papers in the light of what
has just been noted, one finds a distinct similarity in the way he treats the
FitzGerald-Lorentz contraction. I repeat what Poincare said in St Louis in 1904
[P4]. On that occasion he also introduced in essence the first two postulates and
then added, 'Unfortunately, [this reasoning] is not sufficient and complementary
hypotheses are necessary; one must assume that bodies in motion suffer a uniform
contraction in their direction of motion.' One rereads the grand memoir in the
Rendiconti di Palermo [PI] and finds an admirable discussion of the Lorentz
transformation but no mention that these transformations imply the contraction
of rods; the emphasis in that paper is on dynamics. It is likewise the case in a
semipopular account of relativity which Poincare wrote in 1908 [P5].
My own assessment of Poincare's contributions to relativity coincides with what
was said about him during the opening remarks of the meeting in Paris of the
Societe Francaise de Philosophic, referred to earlier: 'The solution anticipated by
Poincare was given by Einstein in his memoir of 1905 on special relativity. He
accomplished the revolution which Poincare had foreseen and stated at a moment
when the development of physics seemed to lead to an impasse' [L6].
- Whittaker and the History of Relativity. In 1910, Edmund Whittaker pub-
lished a book entitled History of the Theories of Aether and Electricity [ W1 ]. This
work covers the period from Descartes to the close of the nineteenth century. Col-
leagues more knowledgeable on this period than I, confirm my impression that it
is a masterpiece. Forty years later, a revised edition of this book came out. At that
time Whittaker also published a second volume dealing with the period from 1900
to 1926 [W2]. His treatment of the special theory of relativity in the latter volume
shows how well the author's lack of physical insight matches his ignorance of the
literature. I would have refrained from commenting on his treatment of special
relativity were it not for the fact that his book has raised questions in many minds
about the priorities in the discovery of this theory. Whittaker's opinion on this
point is best conveyed by the title of his chapter on this subject: 'The Relativity
Theory of Poincare and Lorentz.'* Born had given Whittaker fair warning [B3].
Einstein's reaction was, 'I do not have to read the thing. ... If he manages to
convince others, that is their own affair' [B4].
*Whittaker's obituary of Einstein written for the Royal Society is no work of art either [W3].