Field emission characteristics in He II at temperatures 0.3 < T < 0.8 K and under pressures 10 < P < 25 bar have been used to deduce values of the vortex ring nucleation rate nu in electric fields E of order 3 kV/cm. The values of nu obtained are an order of magnitude larger than those recently determined by Zoll and Schwarz, who employed a completely different technique at the same T and P but with e of order 20 V/cm.