144 THE WATT AND THE TREVITHICK ENGINES. 



year, but now they state 500,000 tons per year. I am to do 

 nothing but wind up the chain for 6eZ. per ton, which is now done 

 by men. They never lift it above 25 feet high. A man will 

 now get up 10 tons for 7s. My engine at Dolcoatli has lifted 

 above 100 tons that height with 1 bushel of coals. I have two 

 engines already finished for this .purpose, and shall be in town 

 in about fifteen days to set them at work. They propose to 

 engage with me for twenty-one years. The outlines of the 

 contract they have sent me down, which I think is on very fair 

 terms. I would thank you for your answer before I leave this 



county. 



i - I am, Sir, 



" Your very humble servant, 



" ED. TREVITHICK." 



In the trial at Dolcoath during his absence the high- 

 pressure steam-puffer whim was beaten by Watt's low- 

 pressure steam vacuum whim-engine as 55 to 120; but 

 having corrected some oversight in the puffer-engine, 

 it then beat Watt as 147 to 35. The trial was to be 

 continued for a month ; and provided the superiority of 

 his whim-engine could be maintained, the adventurers 

 would allow him to apply his high-pressure boilers to 

 their large Boulton and Watt pumping engine. The 

 trial with the whim-engines was for the greatest num- 

 ber of kibbals of mineral raised to the surface by the 

 least consumption of coal. A dispute arose on the dif- 

 ference of the shafts, the one causing more friction to 

 the moving kibbal than the other, when Trevithick 

 agreed to take the worst shaft in the mine. On a trial 

 during sixty-six hours Watt's engine was beaten by 

 more than four times ; and as Trevithick's engine did 

 the work that before required two engines, one of the 

 low-pressure steam Watt engines was removed that the 

 engine working with 40 Ibs. on the inch might perform 

 the whole work. 



