Magnetic Reconnection: Sweet-Parker Versus Petschek

The two theories for magnetic reconnection, one of Sweet and Parker, and the other of Petschek, are reconciled by exhibiting an extra condition in that of Petschek which reduces his theory to that of Sweet and Parker, provided that the resistivity is constant in space. On the other hand, if the resistivity is enhanced by instabilities, then the reconnection rate of both theories is increased substantially, but Petschek's rate can be faster. A different formula from the usual one is presented for enhanced Petschek reconnection.