372 THE QUANTUM THEORYdetermination of e, J. J. Thomson [Tl] had measured the charge of the electron
with the result e = 6.5 X 10~^10! Not until 1908, when the charge of the alpha
particle was found to be 9.3 X 10~^10 [R3] was it realized how good Planck's value
for e was.From the very start, Planck's results were a source of inspiration and bewil-
derment to Einstein. Addressing Planck in 1929, he said 'It is twenty-nine years
ago that I was inspired by his ingenious derivation of the radiation formula which... applied Boltzmann's statistical method in such a novel way' [El]. In 1913,
Einstein wrote that Planck's work 'invigorates and at the same time makes so
difficult the physicist's existence.... It would be edifying if we could weigh the
brain substance which has been sacrified by the physicists on the altar of the [Kirch-
hoff function]; and the end of these cruel sacrifices is not yet in sight!' [E2]. Of his
own earliest efforts, shortly after 1900, to understand the quantum theory, he
recalled much later that 'all my attempts ... to adapt the theoretical foundations
of physics to this [new type of] knowledge failed completely. It was as if the ground
had been pulled from under one, with no firm foundation to be seen anywhere'
[E3].
From my discussions with Einstein, I know that he venerated Planck as the
discoverer of the quantum theory, that he deeply respected him as a human being
who stood firm under the inordinate sufferings of his personal life and of his coun-
try, and that he was grateful to him: 'You were the first to advocate the theory of
relativity' [El]. In 1918 he proposed Planck for the Nobel prize.* In 1948, after
Planck's death, Einstein wrote, 'This discovery [i.e., the quantum theory] set sci-
ence a fresh task: that of finding a new conceptual basis for all of physics. Despite
remarkable partial gains, the problem is still far from a satisfactory solution' [E4].
Let us now return to the beginnings of the quantum theory. Nothing further
happened in quantum physics after 1901 until Einstein proposed the light-quan-
tum hypothesis.
19b. Einstein on Planck: 1905.
The Rayleigh-Einstein-Jeans Law
The first sentence on the quantum theory published by Einstein was written in
the month of March, in the year 1905. It is the title of his first paper on light-
quanta, 'On a heuristic point of view concerning the generation and conversion of
light' [E5, Al]. (In this chapter, I shall call this paper the March paper.) Web-
ster's Dictionary contains the following definition of the term heuristic: 'providing
aid and direction in the solution of a problem but otherwise unjustified or inca-
pable of justification.' Later on, I shall mention the last sentence published by
Einstein on scientific matters, also written in March, exactly one half-century
•See Chapter 30.