  The nucleation of the superconductive phase in macroscopic type-I foils in a
slow, continuously decreasing perpendicular magnetic field is observed to first
occur at the field $H_{c3}$, and reinitiate at $H_{c2}$. The observed variation
of $H_{c2}$ with temperature further yields Ginzburg-Landau parameters for the
materials approximately a factor 2 below tabulations, consistent with previous
determinations in small grains.
