Magnetic reconnection has been studied experimentally in a well-controlled,
two-dimensional laboratory magnetohydrodynamic plasma. The observations ar
e found to be both qualitatively and quantitatively consistent with a gener
alized Sweet-Parker model which incorporates compressibility, downstream pr
essure, and the effective resistivity. The latter is significantly enhanced
over its classical values in the collisionless limit. This generalized Swe
et-Parker model also applies to the case in which a unidirectional, sizable
third magnetic component is present. (C) 1999 American Institute of Physic
s. [S1070-664X(99)92105-5].