by changing the direction of the current flow in one of the two wires.

In core memory, a third wire - the sense/inhibit line - is needed to write or read a bit. Reading uses the process of writing; the X and Y lines are powered in the same fashion that they would be to write a "0" to the selected core. If that core held a "1" at that time, then the magnetic state flips to a "0" and the transition causes a short pulse of electricity to be induced into the sense/inhibit