Sir Arthur Eddington died on 22nd November, 1944. The last sixteen years of his life had been occupied chiefly with the discovery and development of certain new principles in physics, which he used in the first place in order to calculate theoretically the “ Constants of Nature ” (such as the ratio of the mass of the proton to the mass of the electron) ; he did in fact succeed in deriving correctly the values of all those constants of Nature which are pure numbers. Later he showed that his ideas could be presented as a coherent system, to which he gave the name Fundamental Theory, and which may be broadly summed up in the statement: the external world is isomorphous with the square of quaternion algebra.