246 THE QUANTUM [xviii. a
describes simply, in its equations, the relations which connect
the simultaneous variations of directly measurable physical
quantities.” * This attitude of reserve may be prudent, but by
excluding all explanatory theories it “ condemns us to an in
tellectual asceticism.” The human mind cannot permanently
remain satisfied with a mere catalogue of relations, and though
doomed to disappointment in the search, strives to reach a more
comprehensive explanation.
There is no doubt profound truth in the statement of Sir Joseph
Larmor: f “In ultimate logic any physical representation is in
fact a mental construction or analogy, designed to relieve the
mind from the intangible and elusive character of a complex of
abstract relations.” But such a statement should rather encour
age than prohibit attempts at physical representation.
Sir Oliver Lodge has protested against “ a comparatively
recent anti-scientific tendency to teach that we are not making
an attempt to ascertain actual truth about the universe, but
only to formulate propositions that are practically helpful and
convenient.” % Is there then no ultimate scientific certainty ?
Perhaps an answer to this question may be given by adopting
words that have been used in another connection and saying that
natural philosophy provides us with “ an image, in mind, of a
reality previously existing.” The image may vary in different
minds and in different generations, but it seems almost a necessity
of human thought that there must be some reality behind our
imaginings. “ Truth is in the ideal. The actual world is an
approximation thereto. . . . We always aim at truth beyond
the range of our experience or measuring achievements. Absolute
truth may be an unattainable ideal, but it is our clear and
permanent aim.” §
2. The Quantum
The problem of the quantum is not single but complex. In
its inception the quantum theory was concerned with only one
department of physics, but we have come to see that all branches
of physics in which small-scale phenomena are investigated are
concerned with quantum laws. The nature of radiation, the
structure of the atom, the very existence of electric charges and
the characteristics of the electro-magnetic field, all are dependent
upon the quantum or upon quantum principles.
The feature which forces itself upon our attention in con
sidering the quantum is that of discontinuity referred to previously
* See Rougier, Philosophy and the New Physics (Routledge),
t Larmor, Aether and Matter, p. 334.
+ Oliver Lodge, Nature, vol. 119, p. 423, 1927. § loc, cit.