A systematic analysis of the moments of the fragment size distribution has
been carried out for the multifragmentation of 1A GeV Au, La, and Kr on car
bon. The breakup of Au and La is consistent with a continuous thermal phase
transition. The data indicate that the excitation energy per nucleon and i
sotopic temperature at the critical point decrease with increasing system s
ize. This trend is attributed primarily to the increasing Coulomb energy wi
th finite size effects playing a smaller role.