Where this discovery comes from
A current moves a compass
In April 1820 the Danish scientist Hans Christian Ørsted noticed that a compass needle moved when an electric current ran through a wire beside it. That July he published what he found, in a short paper written in Latin.
One thing to hold: A compass, a battery and a length of wire.
Why it matters: It was the first sign that electricity and magnetism are linked. Turn the current round and the needle turns the other way — the start of electric motors and much else.
What we don’t know: It is often told that he saw it by accident during a lecture. Accounts differ about how much he had expected it; his paper is the record.