  The parity nonconserving spin rotation of neutrons in the 0.734-eV p-wave
resonance of $^{139}La$ was measured with the neutron transmission method. Two
optically polarized $^3He$ cells were used before and behind a a 5-cm long
$^{139}La$ target as a polarizer and an analyzer of neutron spin. The rotation
angle was carefully measured by flipping the direction of $^3He$ polarization
in the polarizer in sequence. The peak-to-peak value of the spin rotation was
found to be $ (7.4 \pm 1.1) \times 10^{-3} $ rad/cm which was consistent with
the previous experiments. But the result was statisticallly improved. The s-p
mixing model gives the weak matrix element as $xW = (1.71 \pm 0.25)$ meV. The
value agrees well with the one deduced from the parity-nonconserving
longitudinal asymmetry in the same resonance.
