This is the oldest rotative steam engine in the world. It embodies the four innovations that, together with extended patent protection, Matthew Boulton's capital and entrepreneurship, and James Watt's engineering skill and prudent management, made Boulton and Watt rotative engines the first commercially successful stationary power plants that were independent of wind, water and muscle.
Thomas Newcomen made the first successful steam engines in the early 1700s in England. Their output was reciprocating motion, and they were used mainly for pumping water out of mines. A few powered mills and factories indirectly by pumping water from below a water wheel to above it for re-use.
James Watt's first and most significant innovation was the separate condenser. On each stroke of a Newcomen engine, the cylinder was heated (by steam) and cooled (by a jet of cold water that cooled the steam so that it condensed to water) to create a vacuum so that the atmosphere pushed the piston down. Watt decided to do the condensing in a separate vessel, ensuring that the cylinder remained hot. The separate condenser greatly increased efficiency and thus improved economy.
Watt invented the parallel motion mechanism, which (by replacing a chain) allowed the piston to push the beam up as well as pulling it down. By ensuring the piston rod was constrained to almost truly vertical movement, it allowed the cylinder to be sealed at the top. Thus it enabled power to be doubled without increasing cylinder size.
Boulton and Watt introduced the centrifugal governor to control engine speed. Adapted from mill practice, it was the first feedback device designed for use with engines.
The firm's fourth innovation, sun and planet gearing, was devised after a competitor patented the use of the crank in steam engines, the crank being a simpler mechanism for converting reciprocating to rotative motion. Boulton and Watt could have chosen to share the crucial separate condenser patent with that competitor in return for the right to use the crank; the sun and planet allowed them to maintain their position of never granting licences.
As Boulton and Watt engines were prime movers in the Industrial Revolution, this very significant engine represents not just invention and entrepreneurship, but also wealth creation, mass consumerism, great changes in working life, a massive shift in the use of resources, and consequent damage to the natural environment.
Debbie Rudder, curator, March 2007
On 29 May 2009, the Governor of the Bank of England announced that an image of the Whitbread engine will feature, along with portraits of Boulton and Watt and an image of Boulton's Soho Manufactory, on a fifty pound banknote planned for release in 2010. The selection of our engine for this banknote recognises its significance in both engineering and economic history. (The banknote was released on 2 November 2011, and the Museum's copy is object 2012/6/1.)
Debbie Rudder, curator, June 2009