There is a connected set of events (light-waves) travelling outward from a centre... there are some respects in which all events are alike, and others in which they differ... We must not think of a light-wave as a 'thing', but as a connected group of rhythmical events. The mathematical characteristics of such a group can be inferred by physics, but the intrinsic character of the component events cannot be inferred.

An Outline of Philosophy Ch.15 The Nature of our Knowledge of Physics (1927)