Where we have arrived along this path is brought out in a passage in Eddington's The Nature of the Physical World. There, after describing the modern picture of electrons dancing round the atomic nucleus, he says: 'This spectacle is so fascinating that we have perhaps forgotten that there was a time when we wanted to be told what an electron is. This question was never answered. No familiar conceptions can be woven round the electron; it belongs to the waiting list.' The only thing we can say about the electron, if we are not to deceive ourselves, Eddington concludes, is: 'Something unknown is doing we don't know what.'⁴