Ship's watch, 18th-19th century.
© Science Museum / Science & Society Picture Library
Detail of mechanism. This intricate clock has a bras dial and rack-lever escapement of the type patented in 1792 by Peter Litherland of Liverpool. Its different parts are made from various metals. The springs, chain and cogwheels are the most used parts of the clock and are made from hard-wearing steel. The clock's case is made of bras, an alloy of copper and zinc, and has been coated with gold.