Compasses determine direction based on the Earth's magnetic pull. A compass is crutial for explorers to this day. Without compasses, the Europeans may never have discovered the America's. Could you imagine going on a ship and not knowing which direction you were going?
The compass is the primary device for navigating and direction finding. It was discovered by twelfth century marainers from China and Greece. This wonder-device comes in different forms but the sciences of it remains the same to this day.