POLE STEAM-ENGINE. 105 



may be further tested by the public acts of the time. 

 Lean, an authority on such matters, and certainly not 

 given to unduly praise Trevithick, spoke as follows on 

 the duty of those particular engines at various periods ; 

 and not the least noteworthy is the fact, that Herland, 

 Poldice, and Treskerby, that were prominent in the 

 early use of the Watt engine, threw off their allegiance 

 but shortly before the last days of the great engineer, 

 and converted his low-pressure steam vacuum engines 

 into Trevithick high-pressures. 



"In 1798 Messrs. Boulton and Watt, who on a visit to 

 Cornwall, came to see it ' the Herland engine ' and had 

 many experiments tried to ascertain its duty ; it was under the 

 care of Mr. Murdoch, their agent in the county. Captain John 

 Davey, the manager of the mine, used to state that it usually 

 did twenty millions, and that Mr. Watt, at the time he inspected 

 it, pronounced it perfect, and that further improvement could 

 not be expected. 



"In 1811 the average duty of the three engines (Boulton 

 and Watt's) on Wlieal Alfred Mine was about twenty millions. 

 These engines were at that time reckoned the best in the county. 



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

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

 engine. This engine attained to forty-five millions ; and in 

 1817 it did 46 -9 millions. 



"In 1814 Treskerby engine is reported as doing 17 '48 

 millions. Wm. Sims, engineer. 



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

 pressure pole had been adapted, Lad reached 40 3 millions." 1 



The Herland engine of Watt in 1798 did twenty 

 millions; in 1816 Trevithick's high-pressure pole puffer 

 in the same mine did forty-eight millions. In 1820 

 his high-pressure pole-engine was combined with a 



Lean's ' Historical Account of the Steam-Engine in Cornwall,' pp. 11, 32, 



