  Directed and elliptic flow for the Au + Au system at incident energies
between 40 and 150 MeV per nucleon has been measured using the INDRA 4 pi
multi-detector. For semi-central collisions, the elliptic flow of Z <= 2
particles switches from in-plane to out-of-plane enhancement at around 100 MeV
per nucleon, in good agreement with the result reported by the FOPI
Collaboration. The directed flow changes sign at a bombarding energy between 50
and 60 MeV per nucleon and remains negative at lower energies. The conditions
for the appearance and possible origins of negative flow are discussed.
