We use Cycle 21 Hubble Space Telescope (HST) observations and HST archival ACS
Treasury observations of 30 Galactic Globular Clusters to characterize two distinct
stellar populations. A sophisticated Bayesian technique is employed to simultaneously
sample the joint posterior distribution of age, distance, and extinction for each cluster,
as well as unique helium values for two populations within each cluster and the
relative proportion of those populations. We find the helium differences among the
two populations in the clusters fall in the range of ∼0.04 to 0.11. Because adequate
models varying in CNO are not presently available, we view these spreads as upper
limits and present them with statistical rather than observational uncertainties. Evidence
supports previous studies suggesting an increase in helium content concurrent
with increasing mass of the cluster and also find that the proportion of the first population
of stars increases with mass as well. Our results are examined in the context of
proposed globular cluster formation scenarios. Additionally, we leverage our Bayesian
technique to shed light on inconsistencies between the theoretical models and the
observed data.