A grandfather clock, also called a long case clock or floor clock, is a freestanding, weight-driven, pendulum clock. Its pendulum, which swings back and forth, is kept inside its tower. Clocks of this style are commonly 6 to 8 feet (1.8 to 2.4 meters) tall. The case often features carved ornamentation on the hood, called a bonnet, which surrounds and frames the dial, or clock face. These clocks have a long history. In 1582 the Italian astronomer Galileo Galilei discovered that a pendulum could be used to keep time. He studied pendulum clocks, and drew the first designs for a grandfather clock. In 1656 the Dutch mathematician Christiaan Huygens applied What Galileo had discovered and built the first working grandfather clock (he also patented a pocket watch in 1675.) The first grandfather clocks did not keep time well, often losing as much as 12 minutes a day. In 1670 the English clockmaker William Clement noticed that by making the pendulum in the clock longer he could make the clock keep better time. His longer pendulums required longer cases, Which led to the name “long case” clock, and later grandfather clock. Most grandfather clocks are “striking” clocks, which means they sound the time on each hour.