It is typical of the scientist of the past that he was dependent on phenomena brought about by a highly developed experimental technique for becoming aware of certain properties of the electrical force, whereas for the realistic observer these properties are revealed at once by the most primitive electric phenomena. We remember Eddington's description of the positron as 'negative material', and his subsequent remarks, which show the paradoxical nature of this concept if applied to the hypothetical interior of the atom (Chapter IV). The quite primitive phenomenon of electrical repulsion and attraction shows us the same thing in a manner of which it is not difficult to form a conception.