A compass is a device used to determine direction on the surface of the earth. The most familiar type of compass is the magnetic compass, which relies on the fact that a magnetic object tends to align itself with Earth's magnetic field. Other types of compasses determine direction by using the position of the Sun or a star.
The Lewis and Clark Expedition, also known as the Corps of Discovery Expedition, was the first American expedition to cross what is now the western portion of the United States. It began near St. Louis, made its way westward, and passed through the continental divide to reach the Pacific coast.