Electromagnetic Induction

Induction is not about a magnetic field being present. It is about the flux through a circuit changing. Push a bar magnet into a coil and the galvanometer deflects; hold the magnet still inside the coil and the needle returns to zero; pull it out and the needle swings the other way. The magnet is the same in all three cases, so the field cannot be what matters on its own. What differs is whether the flux linking the coil is changing, and the sign of that change sets the direction of the deflection.

The same rule shows up in several standard set-ups. A metal rod pulled along two parallel rails inside a magnetic field drives a current around the loop it completes. A magnet hung from a spring and set oscillating in and out of a coil below it makes the galvanometer swing left and right with steadily decreasing amplitude, because the induced current removes mechanical energy from the swinging magnet. A bar magnet dropped down a long copper tube falls with an acceleration less than $g$, since eddy currents induced in the tube oppose the motion. An electromagnetic seismograph uses the effect in reverse, turning ground movement into an electric signal.

Two conclusions matter for the paper. An e.m.f. exists only while the flux changes, so a static loop in a steady field produces nothing. And the direction of the induced current is fixed by the field and the motion, never by the metal the wire happens to be made of.