When Michael Faraday made his discovery of electromagnetic induction in 1831, he hypothesized that a changing magnetic field is necessary to induce a current in a nearby circuit. To test his hypothesis he made a coil by wrapping a paper cylinder with wire. He connected the coil to a galvanometer, and then moved a magnet back and forth inside the cylinder.

Click and drag the magnet back and forth inside the coil.

When you move the magnet back and forth, notice that the galvanometer needle moves, indicating that a current is induced in the coil. Notice also that the needle immediately returns to zero when the magnet is not moving. Faraday confirmed that a moving magnetic field is necessary in order for electromagnetic induction to occur.