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The relative cross section for inelastic collisions of the second kind between electrons and mercury atoms in the excited 3P1 state was measured as a function of electron energy. Excited atoms were produced by absorption of the 2537 Å resonance line from a mercury arc. A low-energy beam of electrons was produced using the retarding potential difference method. Scattered electrons which gained kinetic energy were detected by passing them through a potential barrier which reflected unscattered electrons. The data are in good agreement with the cross section computed by applying detailed balancing to the known cross section for excitation to the 3P1 state by electron impact. Information about the angular scattering dependence was also obtained.