CHAPTER XIX.

POLE STEAM-ENGINE.

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