What is a compass actually pointing at?

That time, that place

Physician to Elizabeth I. England was going to sea, and the compass was indispensable — yet no one knew why it points north. Some said the pole star pulled it; some said a great magnetic mountain stood somewhere in the north.

Why this question

Gilbert approached it differently. Rather than looking up for a cause, he decided to build an Earth he could hold.

What was found

He carved a sphere of lodestone and called it a terrella — a little Earth. Then he set a small compass needle on it and moved the needle about.

The needle reproduced exactly what compasses do on the real Earth, right down to dipping downward rather than lying flat as it neared the pole — something sailors already knew.

One conclusion followed: the Earth itself is a great magnet. The cause was not overhead but underfoot. He also distinguished the attraction of rubbed amber from magnetic attraction, and gave that effect a name — the root of our word electricity.