Jonathan Hornblower (1753-1815)
Jonathan (Carter) Hornblower (1753-1815) was an English pioneer of steam power
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. This involved Jabez Carter Hornblower, not Jonathan.
In other developments in steam technology Hornblower was successful and he died a moderately wealthy man.
1815 February 23rd. Died at Penryn
His foundry and works at Penryn flourished for he left a considerable estate, close to £10,000,
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
- Bath Chronicle and Weekly Gazette - Thursday 10 March 1791
- 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