The Watt steam engine was the next great step in the development of the steam engine after the Newcomen engine. A Scottish instrument maker, James Watt arranged a separate vessel for condensing the steam. This condenser, C, was connected with the cylinder through a valve V'. When the piston had reached the top of the cylinder, the valve V was closed and V' was opened. Then the steam rushed from the cylinder into the condenser, which was kept cold and under less than atmospheric pressure. At first these valves V and V' had to be operated by hand, but later, it is said, a boy named Potter, whose job it was to turn these valves, connected the valve handles by cords to the beam ED in such a way that the machine became automatic.

The oldest working Watt engine in the world is the Smethwick Engine, at Millennium Point in Birmingham (formerly at Birmingham Museum of Science & Industry).

See also

• Boulton and Watt