How did Ernest Rutherford’s early device detect electromagnetic waves?

Ernest Rutherford’s early device detected electromagnetic waves by utilizing a magnetized needle. He determined that a magnetized needle would lose some of its magnetization when placed in a magnetic field produced by an alternating current. By observing this loss of magnetization, the needle functioned as a detector for electromagnetic waves.1

Rutherford’s apparatus was noted for being simpler than previous designs and having commercial potential. During his time at the Cavendish Laboratory, he successfully refined the device to increase its sensitivity and range, eventually enabling it to receive signals from a distance of half a mile.1