Eddington's whole intellectual framework was shattered by Dirac's electron equation. The authoritative character of the pronouncements of MTR was hopelessly undermined by the evident falsehood of one of them: that all invariant equations were of tensor form. Relativity had by now become an accepted framework within which both Eddington and this young rising star (Dirac had come to St John's College as an unknown research student in 1923 and was 26 when he discovered the equation) were working. Yet somehow the content of relativity was different from Eddington's original conception.

The second part of this book traces the development of Eddington's ideas from the change of approach brought about by the advent of Dirac's equation to Eddington's attempt at an ordered presentation of his own theory in the first of the two books I have described as constituting the Eddington mystery, Relativity Theory of Protons and Electrons (Eddington 1936), referred to here as RTPE. In this chapter I shall be concerned with the crucial first stage in the development of the theory, for it was at that early stage that the possibility of the calculation of physical constants became apparent to Eddington. It was this that set him off along a path that his contemporaries could not or would not follow.

He came to see the algebraic structures arising from Dirac's original postulation as providing the clue to the union of relativity theory and quantum mechanics. Such a union was devoutly to be wished by many of Eddington's contemporaries in the 1930s.