POLE STEAM-ENGINE. . 73 



with brick flues carrying the heated air under the whole 

 length of the bottom of the boiler, and back again over 

 the top or steam portion for superheating. 



[Rough draft.] 



"CAMBORNE, 28th Ftbruary, 1813. 



"I will engage to erect a puffer steam-engine, everything 

 complete at the surface, on the Cost-all-lost Mine, capable of 

 lifting an 8-inch bucket, 4J-feet stroke, twenty-four strokes 

 per minute, 30 fathoms deep, or 280 gallons of water per 

 minute from that same depth, being a duty equal thereto, for 

 550 guineas. But if a condensing engine, 600 guineas. If of 

 the same size as Wheal Prosper, 750 guineas. 



" RICHARD TREVITHICK." 



The engines, erected in 1811 or 1812, combined the 

 novelty of the steam pole-engine, with the use of high- 

 pressure steam of 100 Ibs. on the square inch, and the 

 comparatively untried principle of steam expansion, 

 carried to what in the present day is thought an ex- 

 treme and unmanageable limit. 



The Wheal Prosper engine fixed near the sea-shore 

 at Grwythian is referred to in Trevithick's note to Mr. 

 Kastrick, 1 as " that new engine you saw near the sea- 

 side, with me, is now lifting forty millions, 1 foot high, 

 with 1 bushel of coal " (84 Ibs.), " which is very nearly 

 double the duty that is done by any other engine in the 

 county." 



This was probably the first application of high-pres- 

 sure steam to give motion to pump-rods. The engine, 

 as compared with the neighbouring Watt low-pressure 

 steam vacuum pumping engines, was small, but the 

 principles of high steam, expansive working, and va- 



See Trevithick's letter, January 26th, 1813, chap, xviii. 



