THE WATT AND THK TRKYTTHTCK ENGIXKS. 175 



his cylindrical boiler, which after years of consideration 

 Dolcoath, in 1811, agreed to. In 1813 he wrote: 

 " That new engine you saw near the sea-side with me 

 is now lifting forty millions, one foot high, with one 

 bushel of coal, which is very nearly double the duty' 

 that is .done by any other engine in the county. A few 

 days since I altered a 64-inch cylinder engine at Wheal 

 Alfred to the same plan, and I think she will do equally 

 as much duty. I have a notice to attend a mine meeting 

 to erect a new engine, equal in power to a 63-inch 

 cylinder single." 1 



The beneficial results of those acts are too large to 

 be here entered into in detail. In round numbers, the 

 early pumping engines of Newcomen did five millions ; 2 

 Trevithick caused them to do ten millions of duty with 

 a bushel of coal. Watt, during thirty years of im- 

 provements, caused the duty to reach sixteen or twenty 

 millions in 1800. Trevithick, on the expiry of the 

 Watt patent, then came into play, and before he had 

 reigned half the time of Watt, again doubled the 

 duty of the steam-engine, as he states in 1813 " his 

 new engine was doing forty millions, being nearly 

 double the duty of any other engine in the county." 

 These statements by Trevithick agree very nearly with 

 the generally-received accounts of the progressive duty 

 of the large pumping steam-engine. 



" In 1798 Davies Gilbert, Esq., and the late Captain Jenkin of 

 Treworgie, found the average of the Boulton and Watt engines in 

 Cornwall to be about seventeen millions. In August, 1811, the 

 eight engines reported averaged 15 '7 millions. During the 

 year 1814 Dolcoath great engine, with a cylinder of 63 inches in 

 diameter, did twenty-one and a half millions nearly. Dolcoath 



1 See Trevithick's letter, January 26th, 1813, vol. ii., p. 55. 



2 See vol. i., p. 41. 



