Ap=(87rV2/C3) hv (8~ p. 2/3h2) sec.-l, is so small that this process is not effective in bringing a spin system into thermal equilibrium with its surroundings. At 300oK, for v= 107 sec.-l, p.= 1 nuclear magneton, the corresponding relaxation time would be 5 X 1021 seconds! However, for a system coupled to a resonant electrical circuit, the factor 87 ('v'/c3 no longer. gives correctly the number of radiation oscillators per unit volume, in unit frequency range, there being now one oscillator in the frequency range v/Q associated with the circuit. The spontaneous emission probability is thereby increased, and the relaxation time redu ced, by a factor f= 3Q'A3/4-rr2V, where V is the volume of the resona tor. If a is a dimension characteristic of the circuit so that V"" a3, and if o is the skin-depth at frequency v, f""'A3/a2o. For a non-resonant circuitf""'A3/a3, and for a< o it can be shown thatf""'A3/ao2•