Dirac, P. A. M. (1927). "The Quantum Theory of the Emission and Absorption of Radiation". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 114 (767): 243. Bibcode:1927RSPSA.114..243D. doi:10.1098/rspa.1927.0039.
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Dirac, P. A. M. (1927). "The Quantum Theory of the Emission and Absorption of Radiation". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 114 (767): 243. Bibcode:1927RSPSA.114..243D. doi:10.1098/rspa.1927.0039.