Jonathan Hornblower (II)
He was born on 5 July 1753 at Chacewater, Cornwall, the sixth child and fourth son of Jonathan Hornblower (1717–1780), steam engine builder, and his wife, Ann Carter. Jabez Carter Hornblower (1744–1814) was his brother.
He was probably educated at Truro grammar school before being apprenticed to a plumber or brazier at Penryn, Cornwall, and lived at Trelever where he was baptized on 25 July 1773.
He was following his trade in 1779 at Penryn when he supplied some copper pipes for the engine at Poldory mine which his father was erecting for Boulton and Watt.
He married Rosamund (either Phillips or Mudge) who died in 1779, and then in 1786 Elizabeth Jordan, who died four years later, leaving two daughters.
He developed a compound engine in 1781 and patented the two stage engine but was prevented from pursuing his invention by litigation with James Watt over the separate condenser, an infringement of his intellectual property. He did install an engine at Radstock near Bath having cylinders 19in. and 24in. in diameter.
1796 Boulton and Watt vs Hornblower and Maberley came to court and BW won their claim for an infringement of their patents.
In other developments in steam technology Hornblower was more successful and he died a rich man.
His foundry and works at Penryn flourished for he left a considerable estate, close to £10,000, when he died at Penryn on 23 February 1815.
A correspondent writes:- The use of the name 'Jonathan Carter Hornblower is a misnomer. Jonathan Jnr. did not possess a middle name as did his brother Jabez Carter Hornblower. There was a Jonathan Carter Hornblower born in the 19th century with whom Jonathan Hornblower born 1753 is often confused. Jonathan married Rosamund Phillips. As to my bona fides, I am a descendant of the Hornblower family and am engaged in writing their history' 
Sources of Information
- BC. 12 Jul 2010
-  Wikipedia
- A Short History of Naval and Marine Engineering by E. C. Smith. Published 1937
-  DNB
- Engineers and Mechanics Encyclopedia 1839: Railways: Early Beginnings