A homogeneous magnetic field beta spectrometer and its completely automatic control system are described. Momentum resolution is such that a monoenergetic line has a full width at half maximum intensity of 0.22%. The instrument was used to analyze the conversion line spectrum of the 411‐kev gamma ray from Hg198. The data give for the conversion ratiosK:L:M:Nvalues of 1:0.361:0.100:0.027; and for (LI+LII):LIII, the value 5.9.