THE WATT AND THE TREVITHICK ENGINES. 



Boulton and Watt engines thirteen years before, as 

 reported by Da vies Gilbert and Captain Jen kin in 

 1708, proving the small inherent vitality of the Watt 

 engine. 



In 1814 the Dolcoath pumping engines, with Trevi- 

 thick's cylindrical boiler and high steam expansion, are 

 thus reported : "The Boulton and Watt, Dolcoath great 

 double .engine, 63-inch cylinder, did a duty of 214 

 millions ; the Shammal 45-inch cylinder, single engine, 

 did 265 millions; and the 63-inch single, Stray Park 

 engine, 32 millions." Shammal engine, nearly 100 years 

 old, beat the Watt engine of more than half a century 

 later ; and so did Stray Park 63-inch, which Watt had 

 laughed at when he first tried his hand as an engineer 

 in Cornwall in 1777. 1 



The marked change in these three engines, while for 

 two or three years under Trevithick's guidance, be- 

 coming more powerful and economical, raised the usual 

 swarm of detractors, and in 1815 a special trial was 

 made, which lasted for two days, to test the reported 

 increased duty by the cylindrical boilers and expansive 

 working. 



The unbelievers were then convinced, and agreed to 

 throw out the Boulton and Watt great double engine 

 63-inch cylinder, together with its neighbour, the worn- 

 out old 45-inch, and put in their stead one engine with 

 a cylinder of 76 inches in diameter, with expansive 

 valve and gear, and parts strong enough and suitable 

 to the high-pressure steam, on Trevithick's promise that 

 it should do more than the combined work of the other 

 two with one-half the coal. 



In 1816 this new engine commenced work, and did 

 forty millions of duty, increasing it during the next 



1 tSec vol. i., p. 30; vol. ii., p. 115. 



