Discovery of Cepheids in IC 4182: Absolute peak brightness of SN IA 1937C and the value of HSUB0/SUB

Repeated imaging of a field in the Sdm galaxy IC 4182 with the Wide Field Camera of the Hubble Space Telescope has led to the discovery of 28 Cepheid variables. The distance modulus to this galaxy, derived from the Cepheids, is (m - M) = 28. 36 +/- 0. 09, and the absolute magnitude at peak brightness of the Type Ia supernova SN 1937C which appeared in IC 4182 is MV_ (max) = - 19. 72 +/- 0. 13. The Hubble diagram using peak V magnitudes of distant (Virgo cluster and beyond) Type Ia supernovae (selected a priori on the basis of light curve and spectral conformity with the prototype) shows an observational random scatter of 0. 36 mag, with evidence that the intrinsic scatter is even smaller. Using the observed scatter to estimate the uncertainty of calibrating the Hubble diagram using only the single calibrating supernova SN 1937C, it is shown that H₀_ = 52 +/- 9km s^-1^ Mpc^-1^.