92 POLE STEAM-ENGINE. 



have raised the steam to 120 Ibs. to the inch, the joints and every- 

 thing perfectly tight. I took the packing out of the stuffing box 

 and examined it, and found that the heat had not at all injured 

 it ; the packing is perfectly tight, not a particle of steam is lost. 



"I have offered to deposit 1000Z. to 5001. as a bet against 

 Woolf 's best engine, and give him twenty millions, but that party 

 refuses to accept the challenge. I have no doubt but that by 

 the time she is in fork she will do 100 millions, which is the 

 general opinion here. The boilers are certainly the best ever 

 invented, as well as the other parts. The draught is the best 

 you ever saw ; I have only one-quarter part of the fire-bars un- 

 covered, yet from one-quarter part of the fire-place that I first 

 made, I find plenty of steam. The greatest part of the waste 

 steam is condensed in heating the water to fill the boiler ; what 

 escapes is a mere nothing. The engine will be loaded, when in 

 fork, about 52 Ibs. to the inch. Now suppose I raise the steam 

 so high at the first part of the stroke as to go so expansive as 

 to leave the steam, at the finish, only atmosphere strong, shall 

 I, in that case, use any more coal than at present ? The mate- 

 rials and joints will stand far more than that pressure ; 500 Ibs. 

 to the inch would not injure them. When the engine gets on 

 two lifts, I will write to you again, and in the meantime please 

 to give me your thoughts on the engine. Every engine that 

 was erecting is stopped, and the whole county thinks of no other 



engine. 



" Your very obedient servant, 



"Bo. TKEVITHICK." 



The new pole puffer-engine worked so satisfactorily 

 and its movements were so manageable that the length 

 of the stroke was increased by the spare 6 inches, which 

 had been allowed as a margin in case of its overrunning 

 its intended stroke. It would bear being worked at 

 eighteen strokes a minute, while the Watt 72-inch 

 engine did not exceed nine strokes a minute ; with 

 steam in the boiler of 80 Ibs. to the inch it performed 

 its work when the steam supply was cut off at two- 

 thirds of the stroke, completing it by expansion. It also 



