"Mr. Woolf, as Mr. Farey states, came to reside in Cornwall about the year 1813, and his 'first engines for pumping water from mines were set up by him in 1814.'"[108] [Footnote 108: 'Phil. Mag. and Annals,' vol. x., p. 97, "Notes on Some Recent Improvements of the Steam-Engine in Cornwall," by W. Jory Henwood, F.G.S.] The foregoing was read at the Philosophical Society in 1831, to refute erroneous statements on the Watt and Trevithick engines. My friend Mr. Henwood had at that time made official experiments in conjunction with Mr. John Rennie on the detail, working, and duty of high-pressure steam Cornish engines, the Watt low-pressure steam principle having been wholly given up. Rees's 'Cyclopædia'[109] also bears the following similar testimony to date of the increased duty:-- [Footnote 109: See Rees 'On the Steam-Engine,' published 1819.] "Trevithick's high-pressure engine was erected in Wales in 1804 to ascertain its powers to raise water. The duty was seventeen millions and a half pounds raised one foot high for each bushel of coals. "The high-pressure steam-engines require a greater quantity of coals, in proportion to the force exerted, than the engine of Mr. Watt, and consequently are not worked with advantage in a situation where coals are dear. "From the reports of the engines now working in the mines of Cornwall, which, with the exception of a few of Woolf's engines, are all on Mr. Watt's principle, and most of them constructed by Messrs. Boulton and Watt, taking the average of nine engines--bad, good, and indifferent together--they were found in August, 1811, to raise only thirteen millions and a half. But when it was known by the engine keepers that their engines were under examination, they took so much pains to improve the effects, that by gradual increase the engines in 1815 lifted twenty-one millions and a half, taking the average of thirty-three engines. In 1816, Stray Park, a 63-inch cylinder, 7 feet 9 inches stroke, single-acting, being one of the three engines on the vast Dolcoath Mine; its performance in four different months was thirty-one, thirty-one and a quarter, twenty-eight, and twenty-eight and a half millions."