  Neutron Scattering measurements for YBa$_2$Cu$_3$O$_{6.6}$ have identified
small magnetic moments that increase in strength as the temperature is reduced
below $T^\ast$ and further increase below $T_c$. An analysis of the data shows
the moments are antiferromagnetic between the Cu-O planes with a correlation
length of longer than 195 \AA in the $a$-$b$ plane and about 35 \AA along the
c-axis. The origin of the moments is unknown, and their properties are
discusssed both in terms of Cu spin magnetism and orbital bond currents.
