THE WATT AND TPIE TREVITHICK ENGINES. 173 



evidence of increased power and economy was imme- 

 diately followed by the application of the same prin- 

 ciples of high-pressure steam and very expansive work- 

 ing to the Watt low-pressure steam vacuum engines at 

 Wheal Alfred, Dolcoath, and other mines, with such 

 satisfactory results as to warrant his offering, on the 

 battle-ground of his first attack on the Watt low-pres- 

 sure steam vacuum principle at Seal-hole in St. Agnes, 

 fourteen years before, 1 at his own pecuniary risk, to so 

 apply those principles in the Wheal Liberty low-pressure 

 steam-engine, which had failed to drain the mine, lift- 

 ing only at the rate of 1880 gallons of water one 

 fathom high at each stroke ; that it should lift an 

 increased quantity of water, and that, too, from an in- 

 creased depth, making the load equal to 5525 gallons, 

 and to perform such increase of work with one-half of 

 the quantity of coal before used ; in other words, he 

 was willing to engage to make the old low-pressure 

 steam-engine perform by its conversion into a high- 

 pressure steam-engine threefold its original work, and 

 also to increase its duty or economic value sixfold ; rest-- 

 ing his argument on the similar changes, then to be 

 seen in operation at Wheal Alfred Mine, and especially 

 in the Watt 63-inch double-acting engine at Dolcoath, 

 whose history we have been tracing. Well might Sir 

 Charles Hawkins hesitate to believe what the experience 

 of sixty years has barely sufficed to make plain to us. 



" CAPTN. TREVITHICK, "PENZANCE, March 27th, 1813. 



" Sir, In consequence of the conversation that has 

 passed between you and West Wheal Tin Croft adventurers, 

 the said adventurers have resolved to put an engine on that 

 mine, agreeable to the proposals offered by you; that is, the 

 engine shall be capable of lifting a 5-inch bucket, 50 fathoms, 



1 See vol. i., p. 90. 



