My present talk has been ranged under ‘applied mathematics’ whereas my work in teaching and research is devoted to the science of physics. The great rift that has torn that science into two camps has hardly been more sharply defined than in the organisation of the talks to be presented at this scientific congress, which had to get through such enormously extensive material that it may be described as a flood, or to preserve local colour, as a Niagara of scientific talks. I am referring to the division into theoretical and experimental physics. While as a representative of theoretical physics I have been put into Section A for normative science, experimental physics turns up only much later under Section C for physical science. In between there are history, linguistics, literature, theory of art and theory of religion. Across all this the theoretical physicist must reach out his hand to his experimental colleague. We shall therefore not be able completely to avoid the question whether it is justified to divide science in general into two portions, and physics in particular into theoretical and experimental.