162 THE WATT AND THE TREVITHICK ENGINES. 



fire-door, 9 feet wide, and 7 feet thick in fire," 1 which he 

 proposed to replace in 1806 by a cylindrical boiler to 

 give steam of 25 Ibs. on the inch. 



Pooly also saw the finishing stroke in 1811, when 

 the boilers still known as the Trevithick or Cornish 

 boilers, gave steam to the three engines ; after a twelve 

 years' fight between low and high pressure, commencing 

 with Trevithick's globular boiler and internal tube, in 

 Dolcoath, in the year 1799, from which time it gained 

 step by step, though in comparatively small engines, up 

 to 1811, when the cylindrical boilers took the place of 

 the condemned hearse and globular boilers, and gave 

 really strong and expansive steam to the three Dolcoath 

 pumping engines that from time immemorial had been 

 rivals, causing all three of them to lift an increased 

 quantity of water, and at the same time to save one-halt 

 in the cost of coal ; this continued for four or five years, 

 when in 1816 the 63-inch double and the 45-inch, being 

 the youngest and the oldest of the three, were removed, 

 that a new 7 6-inch cylinder, better adapted to Trevithick's 

 expansive steam might more cheaply perform their joint 

 work. Prior to this change the three engines were 

 known by the names Shammal 45-inch, formerly Bullan 

 Grarden, 2 but before that as Oarloose, of the period and 

 form of the Pool engine ; 3 Stray Park 63 single, 

 formerly Wheal Gons, 4 dated from 1770 to 1777; and 

 the 63-inch double of Watt in 1780. 



" SlR, " DOLCOATH MINE, March 29M , 1858. 



"I have obtained the following information respecting 

 the building of the first cylindrical boilers, as ordered by your 

 late father for Dolcoath ; and some information of the results 



1 See Trevithick's letter, February 18th, 1806, vol. ii., p. 143. 



2 See vol. i., p. 25. 3 See vol i., p. 5. 



4 Onprv Ttnn7p QrvVlrnn nf liv Smilne 



Query Bonze, spoken of by Smiles. 



