Return to Cornwall, 1810--Wheal Prosper pole vacuum engine, 1811--Cylindrical boilers, 1811--Steam pressure, 100 lbs.--Duty of engine, 40 millions--Expansive working, 1811--Herland high-pressure pole puffer, 1815--Steam pressure, 150 lbs.--Boiler making--Comparison with Watt's engine--Blue-fire--Steam--Patent specification--Steam-ring stuffing box--Engines in Lima--A 33-inch pole-puffer more powerful than a 72-inch Watt engine--Description of pole engine and boilers--Trevithick's calculation--Trial of Herland engines--Steam-cushion--Power of the pole-engine--Defective workmanship--Sims examines the pole-engine--Opposition from shareholders--Defective boilers--Challenge to Woolf--Davies Giddy's opinion--First cost, and cost of working one-third of the Watt engine--Meeting of opposing shareholders--Duty of the high-pressure steam pole puffer-engine, 1816--Comparison with the Watt engine--Combined high-pressure pole and cylinder for expansion--Wheal Alfred Watt engine converted to high pressure--Wheal Chance combined engine--Mr. Michael Williams's opinion--Woolf and Trevithick Page 69-113 CHAPTER XX. THE WATT AND THE TREVITHICK ENGINES AT DOLCOATH. Early steam-engines--Semicircular boiler, 1775, net power 7 lbs. on the inch--Watt's statement in 1777--Engines in Dolcoath--Watt's engine, 1778--Watt's engine at Herland, 1798--Trevithick's tubular boiler, 1799--Reconstruction of the Carloose 45-inch, 1799--Gross and net power of engines--Comparison of Newcomen, Watt, and Trevithick engines--Boiler explosion, 1803--Strong rivalry with Watt--Locomotive at Coalbrookdale, 1803--Watt's proposed locomotive--Competition in Wales--Numerous high-pressure engines, 1803--Patent difficulty--Watt's opposition, 1804--Government inquiry--Competitive trials in Wales--Tramway locomotive, 1804--The bet--Opposition because of saving of labour--Worcester engine--West India Docks engine--High-pressure steam condensing engines--One or two cylinders for expansion--Sirhowey boilers--Mr. Homfray's opinion of the Watt opposition--Mr. Whitehead makes engines in Manchester--Cylindrical tubular boiler in Wales for large engines, 1805--Watt contests at Dolcoath, 1805--Steam-blast--Superiority of high-pressure whim-engines--Proposed boiler for the large pumping engine, 1806--Steam pressure--The Watt boiler--Comparison of size of fire-place and coal used--Dredger contract--Theory of steam--Trevithick's Dolcoath boiler when applied to the Watt engine, with expansive gear, to save 300l. monthly, 1806--Momentum of pumping engine--Continued tests of high and low pressure whim-engines at Dolcoath--Watt engine put aside, 1806--High-pressure engines ordered, 1806--High-pressure pumping engine for Wheal Abraham, 1806--Disputed patent right--Expansion reduces heat--Boiler for the Watt 63-inch engine, 1806--Cost of Trevithick's boiler--Advantage of small tubes in boilers--Trinity