Planck’s Cosmic Harmonium 265
overlapped with the deaths of three of his most important colleagues, leaving him as the
sole remaining professor of physics in Berlin by the end of 1894. Arguably, Planck ’ s return
to issues of thermodynamics and black-body radiation in that year was affected by the
sudden loss of many of his Berlin colleagues, which required him to take up these other
physical investigations after their demise. Helmholtz ’ s death effectively forestalled any
awkward controversy between teacher and student on the musical issues that mattered so
much to both of them.
This was, indeed, the first occasion on which Planck could have experienced what he
much later described in his autobiography as a generality that has come to be called
“ Planck ’ s principle ” : “ A new scientific truth does not triumph by convincing its opponents
and making them see the light, but rather because its opponents eventually die, and a new
generation grows up that is familiar with it. ”^29 Though Planck remarks this in the immedi-
ate context of the struggle between Boltzmann and Wilhelm Ostwald about the reality of
atoms, his comment immediately follows his description of his musical experiments. We
lack documentary evidence about the conversations between Helmholtz and Planck in the
aftermath of his 1893 work on tuning, but they may have been strained and awkward,
given Planck ’ s well-known deference to authority, and to Helmholtz in particular. Helm-
holtz ’ s passing gave way to new voices expressing contrary views, as had Planck. Those
onerous encounters with death in the “ black year ” of 1894 provided a forceful education
in dimensions of historicity, which Planck received first of all during his musical struggle
with tuning and convention.
Planck certainly confronted these issues as he participated in the controversy about the
reality of atoms, during which he changed his views toward those of Boltzmann, a pas-
sionate advocate of real (rather than purely theoretical) atoms and the great champion of
their statistical nature. During the years 1894 through 1900, Planck ’ s research on the
equilibrium radiation of black bodies turned on the application of Boltzmann ’ s methods.
As with his work on the Eitz harmonium, Planck combined his underlying theoretical
preoccupations with the external demands of practicality: an electric lightbulb manufac-
turer had requested help determining the optimal radiance for their product, which in turn
devolved on thermodynamic and electrodynamic questions that had emerged already by
1859, when Gustav Kirchhoff had devised and named the idealization of heating a perfectly
black oven to a given temperature, allowing some of its radiant light to escape through a
small hole for observation. Kirchhoff had established that this “ black-body radiation ” was
universal in terms of its distribution of energy over frequency, depending only on the oven ’ s
temperature, and not its size, shape, or materials. Because of this absolute quality charac-
terizing the energy distribution, Planck was interested in finding what determined the exact
shape of that distribution, which was becoming ever better known through the efforts of
his experimental colleagues in Berlin.
Approaching this problem, Planck brought to bear the thermodynamics of entropy that
he had developed in his earlier work. But two elements of his treatment had distinctly