  We have used deep HST/WFPC2 images in V (F606W) and I (F814W) to measure the
luminosity distribution of the globular clusters in NGC 4874, the central cD
galaxy of the Coma cluster. We find the ``turnover'' point of the globular
cluster luminosity function (GCLF) to lie at V = 27.88 +/- 0.12, while the
overall GCLF shape matches the standard Gaussian-like form with dispersion
SIGMA_V = 1.49 +/- 0.12. We use the GCLF as a standard candle by matching the
turnover points in NGC 4874 and another Coma elliptical, IC 4051, with those of
the giant ellipticals in the Virgo cluster (M87 and five others). The result is
(m-M)_(Coma - Virgo) = 4.06 +/- 0.11 magnitudes, which converts to a Coma
distance d = 102 Mpc if the Virgo distance modulus is (m-M)_0 = 30.99 +/- 0.04.
The Hubble constant which emerges from our GCLF measurement is then H0 = (69
+/- 9) km/s/Mpc. We confirm this H0 value with a novel presentation of the
``Hubble diagram'' for GCLFs in giant E galaxies. Measurements of additional
GCLFs in the Coma ellipticals, as well as calibrating galaxies in Virgo and
Fornax, have excellent potential to refine this result in the near future.
