POLE STEAM-ENGINE. 101 



similar in general construction to the Wheal Prosper 

 pole-engine, but still more simple from the absence of 

 air-pump and condenser, did as much work as three 

 of Watt's largest engines with cylinders of 72 inches 

 in diameter. This great stride in the useful value of 

 the steam-engine was forced on the public by Trevi- 

 thick's single-handed energy, when every man was 

 against him, even Henry Harvey, his brother-in-law 

 and friend, his former partner, Andrew Vivian, and 

 his once carpenter and assistant, Arthur Woolf. As 

 a closing attempt to finally crush him, he was made 

 personally responsible for the payment of an engine 

 erected for the benefit of others. This was the great 

 trial test of the power and economy of the purely high- 

 pressure expansive steam-engine as compared with the 

 Watt low-pressure vacuum engine applied to large 

 pumps. 



" SIR, " HAYLE FOUNDRY, 18th April, 1816. 



" I was at Herland to-day. Captain Grose received 

 a letter while I was there, signed by Captain William Davey 

 and Joseph Vivian, requesting him to appoint others to attend 

 the trial of the engine, as it would not be convenient for them 

 to do it. 



" Captain Samuel Grose, jun., brought down the drawing for 

 your engine. He said he had taken off the working gear only. 

 If you would wish it, we will make the working-gear and all 

 the wrought-iron work on the drawing for the two engines 

 ordered, and will take on a man or two immediately for that 

 purpose. You will let me know about this before you set off, 

 and also if any alteration is to be made in the beam for Wheal 

 Treasure engine, since you have altered the size of the pole. 

 We had cast the case, but I suppose it will suit some place else. 



" Your obedient servant, 



"HENRY HARVEY. 



" MK. I!K'IIAI;I TuKvmucK." 



