176 THE WATT AND THE TREVITHICK ENGINES. 



Shammal engine, with a cylinder of 45 inches in diameter, did 

 twenty-six and three-quarter millions. Dolcoath Stray Park 

 engine, with a cylinder of 63 inches in diameter, did thirty-two 

 millions. 



"In 1815 a trial was made, to prove the correctness of the 

 monthly reports. Stray Park engine at Dolcoath was chosen for 

 the purpose, because its reported duty was such as led some 

 persons to entertain doubts of its accuracy. The trial was con- 

 tinued for ten days, to the full satisfaction of all concerned. 



"In 1816, Jeffrie and Gribble erected a new engine, 76-inch 

 cylinder, single, at Dolcoath, which did forty millions. This was 

 the first instance of such duty having been performed by an 

 engine of that simple construction. 



"In 1819, Dolcoath engine performed the best during this 

 year, and at one time reached forty-eight millions. 



" In 1820, Treskerby engine, to which Trevithick' s high- 

 pressure pole had been adapted, reached 40 3 millions. 



"In 1816, Sims also erected an engine at Wheal Chance, to 

 which he applied the pole adopted by Trevithick in his high- 

 pressure engines. This engine attained to forty-five millions. 



" In 1828 public attention had now been attracted to the 

 improvements which Captain Grose had introduced into his 

 engine at Wheal Towan. The duty of this engine, in the month 

 of April this year, equalled eighty-seven millions. 



" This again gave rise to suspicions of error in the returns. 

 This engine was accordingly subjected to a trial (as Stray Park 

 engine had been in 1815), which was superintended and con- 

 ducted by many of the principal mine agents, engineers, and 

 pitmen of other mines. 



" The quantity of coal consumed in 1835, compared with the 

 quantity that would have been consumed by the same engines in 

 the same time, had they remained unimproved from the year 

 1814, shows that the saving to the county amounts to 100,000 

 tons of coal, or 80,000?. sterling per annum." l 



Lean seems to have calculated on a bushel of coal 

 as 94 Ibs. In 1798, when Trevithick was about to give 



1 Lean's ' Steam-Engine in Cornwall.' 



