1858

Big Ben

Benjamin Hall (1802–1867)

Big Ben is a clock tower in London that holds one of the largest chiming clocks in the world. In 1858, civil engineer Benjamin Hall was the Commissioner of Works, and he supervised the installation. What makes this clock so interesting from an engineering perspective is its massive scale, as well as, from a social standpoint, its function as a public fixture helping a rapidly industrializing city become conscious of time.

Big Ben’s clock starts with a massive pendulum, 13 feet (4 meters) long, a scaled-up version of the original mechanical pendulum clocks. With this length, the period of the pendulum, or the time it takes to swing from right to left and back to the right, is 4 seconds. To precisely adjust this pendulum to account for temperature changes, pennies are added to the top of it. Each penny adjusts the clock by 0.4 seconds per day. The pendulum weighs 682 pounds (310 kg).

The pendulum controls the escapement. The escapement lets energy escape from a falling weight and allows the clock’s gear train for the hands to move forward one increment. The escapement also supplies the energy that keeps the pendulum swinging. Big Ben was the first clock in the world to use the double three-legged gravity escapement, which was invented specifically for Big Ben and is particularly reliable.

The energy for the clock comes from a half-ton weight attached via a cable to a winding drum. Clock engineers wind the clock three times a week. The rotation from the escapement feeds into the clock’s gear train for the hour and minute hands. The hands are immense; the minute hand is 14 feet (4.2 meters) long and weighs 220 pounds (100 kg). A single shaft rises from the clock’s gear train to a gear that sends power down four shafts to the four clock faces.

There are two other weights and two other gear trains in the clock. One gear train controls the hammer for the main bell that counts the hours. The other gear train controls the hammers for the four smaller bells, which play the little song “Westminister Chimes” every quarter hour.

SEE ALSO Mechanical Pendulum Clock (1670), Atomic Clock (1949), Atomic Clock Radio Station (1962), LCD Screen (1970).

Big Ben is the third-tallest freestanding clock tower, and ushered in the Industrial Revolution by chiming for the entire city.