Original Bill, submitted by Jonathan Enys to Jonathan Hornblower, for materials and labour used at “Mr. Hornblower’s Mill” during the first half of 1796. 1 page 13 x 8 inches, marginal defects. 1796. Jonathan Hornblower (17531815), pioneer of steam power. He developed a compound engine in 1781 but was prevented from pursuing his invention by litigation with James Watt His compound steam engine principle was not revived until 1804 by Arthur Woolf. Following the expiration of Boulton and Watt’s patent, Hornblower’s compound steam engine principle contributed significantly to the increases in steam engine efficiency. He invented the double-beat steam valve in around 1800. In other developments in steam technology, however, he was more successful and he died a rich man at Penryn in 1815. He is buried in St Gluvias churchyard.