  We present 3 methods for measuring the Galactic dust extinction law slope R_V
and a method for quantifying fine structure in dust clouds in the direction of
differentially-reddened globular clusters. We apply these methods to the low-
latitude globular cluster NGC4833 which displays variable extinction/reddening
about a mean <A_V> ~ 1. A set of Monte Carlo simulations is used to
characterize the efficacy of the methods. The essence of the first 2 methods is
to determine, for an assumed value of R_V, the relative visual extinction
delta(A_V) of each cluster horizontal branch (HB) star with respect to an
empirical HB locus; the locus is derived from the CMD of a subset of stars near
the cluster center in which differential reddening is small. A star-by-star
comparison of delta(A_V) from the (B-V,V) CMD with that from the (V-I,V) CMD is
used to find the optimal R_V. In the third method, R_V is determined by
minimizing the scatter in the HB in the (B-V, V) CMD after correcting the
photometry for extinction and reddening using the Schlegel et al. (1998) dust
maps. The weighted average of the results from 3 methods gives R_V = 3.0 +/-
0.4 for the dust towards NGC4833. The dust fine structure is quantified via the
difference, Delta(A_V)_ij = [delta(A_V)]_i - [delta(A_V)]_j, between pairs of
cluster HB stars (i,j) as a function of their angular separation r_ij. The
variance of Delta(A_V)_ij is found to have a power- law dependence on angular
scale: var(r) \propto r^(+0.9 +/- 0.1). This translates into an angular power
spectrum P(kappa) \propto kappa^(-1.9 +/- 0.1) for r ~ 1' - 5', where kappa =
1/r. The dust angular power spectrum on small scales (from optical data)
matches smoothly onto the larger-scale power spectrum derived from Schlegel et
al.'s far-infrared map of the dust thermal emission.
