Boulton and Watt are most well known for their development of the steam engine. Boulton and Dr Small had started experimenting with steam at the watermill powered Soho Factory as a way of providing power when there was less water during the dry season. Boulton wrote of his “Fire Engine” to Benjamin Franklin:
“My engagements since Christmas have not permitt’d me to make any further progress with my fire engine, but as the thirsty season is approaching apace, necessity will oblige me to set about it in good ernest.”
[Letter. Matthew Boulton to Benjamin Franklin, Feb 1766. MS 3782/12/1/2]
The intention was to pump water back up stream and increase the flow of water passed the mill, but this was not very efficient. Watt started experimenting with steam, but it was after being asked to repair a model of a Newcomen Steam engine that his experiments led to success. This led him to invent a steam engine with a separate condenser from the cylinder in 1765, far more efficient than its Newcomen counterpart. Boulton was instrumental in gaining an extension of the condenser’s patent for another 25 years in 1775. With a basis for profit secured Boulton and Watt’s partnership began in the same year.
Initially the engines were designed for pumping water, but attention was soon paid to those that could power the machinery. The above image is one of the first Sun and Planet Engines and the drawing was by Watt, although the initial invention was by the Soho manufactory engineer William Murdoch (1754 to 1839). The Sun and Planet Engine was so called because of the way the two cogs on the wheel rotated around each other, much like a planet around the sun. This was used so as to avoid a method patented by James Pickard which used cranks to turn the steam engine’s motion into a circular force.