that it could be exhausted to atmosphere without reliance on a vacuum to enable it to perform useful work. Ewing states that Watt's condensing engines were known, at the time, as low pressure compared to high pressure, non-condensing engines of the same period.

Watt's patent prevented others from making high pressure and compound engines. Shortly after Watt's patent expired in 1800, Richard Trevithick and, separately, Oliver Evans in 1801 introduced engines