  A low concentration of columnar defects is reported to transform a
first-order vortex lattice melting line in BSCCO crystals into alternating
segments of first-order and second-order transitions separated by two critical
points. As the density of CDs is increased, the critical points shift apart and
the range of the intermediate second-order transition expands. A third, low
temperature critical point was also observed in one sample. The measurement of
equilibrium magnetization and the mapping of the melting line down to 27K was
made possible by employment of the shaking technique.
