  The geometric resonance of open orbits in unidirectional lateral
superlattices has been examined with high magnetic-field resolution.
Magnetoresistance oscillations periodic in 1/B, analogous to the well-known
commensurability oscillations but orders of magnitude smaller both in magnitude
and in the magnetic-field scale, have been observed superposed on the low-field
positive magnetoresistance. The periodicity in 1/B can be interpreted in terms
of higher order resonances.
