After coming across an article by Schwinger where he tries to deduce the spin of a neutron, I started to wonder when the same thing was done for the photon... Specifically, I've been trying to locate "the" article where the spin of the electromagnetic field was theoretically determined to be 1 (though I'd also settle for "an" article). I know that photons were known to obey Bose-Einstein statistics even before those statistics had a name, but as I understand it, it wasn't until Pauli's 1940 paper that the connection between spin/statistics was established, and even then that would only establish that it had an integral value. I say "theoretically" because presumably it could have been determined experimentally in early experiments (ala Compton) from momentum conservation, but that's not very interesting; we could have known the same for electrons, but we'd still cite Dirac as the one who established it theoretically; so I'm looking for X where Electron Spin: Dirac :: Photon Spin:X. The trouble is most articles now treat the photon spin of 1 as a self-evident fact based upon the vector-nature if the wave equation, or via the irreducible representation theory of the Lorentz group...but that doesn't seem like it would have been that obvious in the 20's/30's (though if it was, I'd love to see the papers).