Are electricity and magnetism strangers?

That time, that place

It happened during a lecture at Copenhagen. Ørsted was setting up to run current through a wire when the compass needle lying on the table moved.

Why this question

This was not supposed to happen. That electricity and magnetism are separate phenomena was firm common sense; Gilbert had distinguished them two centuries before.

Both attract and repel, the settled view held, but neither affects the other.

What was found

What took him months to pin down was not the motion but its direction.

The needle was not drawn toward the wire or pushed away from it. It turned to wrap around the wire. The force was tracing a circle rather than the straight line between two bodies.

Every force known until then acted along a straight line — gravity, electric attraction, magnetism. A circling force was new.

Word crossed Europe within months, and Ampère soon put it into equations.