In this paper I attempt to trace certain aspects of the evolution of theories of space-time and mechanics as revealed by a brief comparative study of Newtonian theory, Robb's theory, general relativity, and Milne's kinematical relativity. The first object is to emphasise how each theory leaves us in a position in which the succeeding one appears as a perfectly natural next step in the development of ideas. The second object is to show how, in spite of superficial differences in character, (...) the theories all necessarily possess the same general structure constituted by the presence of hypotheses, from which certain general mathematical relations are deduced, which in their turn are used to predict relations between observable quantities. (shrink)

This is a subject of recurrent interest which calls for review from time to time; I believe the last word upon it can never be said. Several topical reasons might be cited for attempting to deal with it at the present time, but these could not be pursued to the relevant applications in such a short discussion. In fact the subject is obviously a difficult one to deal with at all briefly since it is so closely bound up with other (...) large subjects—causality, space–time, and so on. (shrink)