The man in the street to-day is aware that recent developments in the physical sciences have necessitated a fundamental revision of the concepts of physics; he finds that Einstein is no less upsetting to his ideas than was Copernicus to those of his own time or than Darwin was to Bishop Wilberforce. The plain man who has “ philosophical leanings ” is aware that questions previously regarded as metaphysical—and about which philosophers have written much that is unintelligible—are now recognized as (...) falling within the scope of physics. Every reader of this Journal is aware that the criticism to which the main concepts of physics—space, time, matter—have been subjected is so fundamental that it is no longer possible to say that there are material bodies in space, which have events happening to them at a given time. We must substitute the conception of a fourfold continuum within which space, time and matter are inextricably involved. Finally, we are told that this new way of regarding the classical trinity suggests the consequence that we know nothing about the “ inner nature ” of the terms with which we deal, we can make no assertions as to the ultimate nature of that to which they may refer. In this respect the prevailing temper of the present-day scientist is to be contrasted with the cocksureness of most nineteenth-century physicists l who, even if they did not go so far as to say “ we know what matter is,” at least suggested that only the metaphysician had, or could have, any doubts as to its nature and reality^. (shrink)