  As deeper observations discover increasingly distant galaxies, characterizing
the properties of high-redshift galaxy populations will become increasingly
challenging and paramount. We present a method for measuring the clustering
bias of high-redshift galaxies from the field-to-field scatter in their number
densities induced by cosmic variance. Multiple widely-separated fields are
observed to provide a large number of statistically-independent samples of the
high-redshift galaxy population. The expected Poisson uncertainty is removed
from the measured dispersion in the distribution of galaxy number counts
observed across these many fields, leaving, on average, only the contribution
to the scatter expected from cosmic variance. With knowledge of the Lambda Cold
Dark Matter power spectrum, the galaxy bias is then calculated from the
measured cosmic variance. The results of cosmological N-body simulations can
then be used to estimate the halo mass associated with the measured bias. We
use Monte Carlo simulations to demonstrate that Hubble Space Telescope pure
parallel programs will be able to determine galaxy bias at z>~6 using this
method, complementing future measurements from correlation functions.
