XVIII. I] INTERPRETATION OF THE QUANTUM 245
The marvellous method, due to C. T. R. Wilson, of rendering
visible and of photographing the track of a single atomic pro
jectile or a single electron; the scintillations due to alpha
particles observed in the spinthariscope of Crookes ; the beautiful
experiments of Rutherford and Geiger in which these particles
are counted by an ionization method; all these afford convincing
evidence for the existence of discrete entities which may be called
atoms of matter or of electricity.
More recent photographs taken by Wilson’s method, in
particular those showing the ionization produced by a beam of
X-rays, might almost be said to reveal the existence of quanta, or
at least to afford such striking evidence in their favour that even
the most sceptical must find it hard to disbelieve.
The controversy between the Realist and the Idealist schools
of philosophy which has long been raging is reflected in the
antagonistic views of scientific workers. British physicists,
inspired by the genius of Newton and influenced by many later
teachers, have long sought to develop a mechanical theory of
natural phenomena. They have been accustomed to work by
means of mechanical models, and as is well known both Faraday
and Maxwell made extensive use of such models.
Opposed to this procedure is what may be called the
Continental method, which does not attach great importance
to models, but prefers to work after the manner of the pure
mathematician by means of abstract symbols. Instead of
dealing with “ action through a medium,” investigators of this
school recognize “ action at a distance ” and develop the
consequences of that view.
To quote again from Schuster : “ Those who believe in the
possibility of a mechanical conception of the universe and are
not willing to abandon the methods which from the time of
Galileo and Newton have uniformly and exclusively led to
success, must look with the gravest concern on a growing school
of scientific thought which rests content with equations correctly
representing numerical relationships between different phenomena,
even though no precise meaning can be attached to the symbols
used. The fact that this evasive school of philosophy has
received some countenance from the writings of Heinrich Hertz
renders it all the more necessary that it should be treated seriously
and resisted strenuously.”
On the other hand we have such a statement as “Maxwell’s
theory is contained in Maxwell’s equations,” and we meet those
who regard the idea of a real kinetic theory of matter—at one
time firmly believed in—as a “ mirage.” Influenced by the
philosophy of “ positivism ” there is “ a school of physics that
takes no interest in a mechanism explaining the phenomena, but