theoretical physicists worked to preserve the centrality of mechanical laws of
bodies, a paradigm which had led to so many past advances into new research
areas by introducing strategic modifications. The most successful of these was
Planck, whose quantum theory in 1900 abandoned classical dynamics in
postulating abrupt changes in energy levels; on this basis Einstein’s special
relativity in 1905 explained anomalous features of light, and Bohr in 1913
developed a theory of atomic structure.
Heated debates took place between the camps (Lindenfeld, 1980: 80–86,
105–110; Johnston, 1972: 181–8; EP, 1967: 7:15). Planck and Boltzmann,
whose statistical mechanics provided the basis for Planck’s defense of atomism,
disputed repeatedly with Ostwald and Mach during 1895–1905. Neo-Kantians
joined the battle, pointing out that Mach’s extreme inductivism was unable to
account for the theoretical aspects of science, its ability to predict the future,
and its mathematical laws. Mach in turn rejected the a priori character of
number, holding that the integers arose from the practical needs of calculation.
Mach acquired a reputation as a naturalistic extremist by arguing that the
simplest unification of the science occurs under the auspices of physiology:
sensations in the nervous system are the only reality, and economy of thought
is itself an adaptation of the organism to its environment. This reduction to
physiological psychology raised echoes of the Neo-Kantian debates of the
1860s and 1870s over the physiological interpretation of the a priori catego-
ries, and gave energy to the renewed rejection of psychologism and the defense
of objectivity in mathematics by Frege and Husserl. Planck from 1908 through
the 1920s defended a version of Kantianism against Mach’s reduction of reality
to a flow of sensations; like Cassirer and the Neo-Kantians, Planck regarded
Mach’s position as relativistic subjectivism. These debates were a dress rehears-
al for the Vienna Circle’s campaign to drive metaphysics off the stage. So far
it was a struggle over what is legitimate within physics; later it became a
question of what is legitimate in any field of reason.
That movement began to crystallize during the uproar of public fame about
Einsteinian relativity theory, following Eddington’s astronomical evidence of
the bending of light in 1919. In this vein was the publicity which surrounded
Bohr’s Copenhagen school and Heisenberg’s quantum mechanics with its in-
determinacy principle, announced in 1925. Philosophy was not simply re-
sponding to new discoveries in physics, however; similar problems had existed
since Einstein’s special theory of relativity in 1905, and even earlier, without
upsetting the dominance of Neo-Kantian interpretations over Machian pheno-
menalism. Although verification was exemplified for both Schlick and Popper
by the relativity verification, it was not the only interpretation. Eddington
himself, the experimental verifier, hardly took it as grounds for rejecting
metaphysics or for demarcating true science from pseudo-science, and even722 •^ Intellectual Communities: Western Paths