Reprinted in
(translation into Russian) Einsteinovskij Sbornik 1984-1985, s. 215, M., Nauka, 1988.
Selected Papers on Quantum Electrodynamics, editor J. Schwinger, Dover Publications, Inc., New York (1958) 1.

Summary
The problem is treated of an assembly of similar systems satisfying the Einstein-Bose statistical mechanics, which interact with another different system, a Hamiltonian function being obtained to describe the motion. The theory is applied to the interaction of an assembly of light-quanta with an ordinary atom, and it is shown that it gives Einstein's laws for the emission and absorption of radiation. The interaction of an atom with electromagnetic waves is then considered, and it is shown
that if one takes the energies and phases of the waves to be q-numbers satisfying the proper quantum conditions instead of c-numbers, the Hamiltonian function takes the same form as in the light-quantum treatment. The theory leads to the correct expressions for Einstein's A's and B's.

Related references More (earlier) information appears in P. A. M. Dirac, Proc. Roy. Soc. A111 (1926) 281;
P. A. M. Dirac, Proc. Roy. Soc. A113 (1926) 621;
P. A. M. Dirac, Proc. Roy. Soc. A112 (1926) 661;
See also M. Born, Z. Phys. 38 (1926) 803;
M. Born, Nachr. Gessel. d. Wiss. Gottingen, (1926) 146;
O. Klein and Rosseland, Z. Phys. 4 (1921) 46;
A. Einstein and P. Ehrenfest, Z. Phys. 19 (1923) 301;
W. Pauli, Z. Phys. 18 (1923) 272;
F. London, Z. Phys. 40 (1926) 193;
P. Jordan, Z. Phys. 40 (1926) 809;
M. Born, Z. Phys. 40 (1926) 167;

Record comments
First steps in quantum field theory. Invention of the second quantization method.