THE WATT AND THE TREVITHICK ENGINES. 157 



ceding the downfall of the Watt low-pressure steam 

 vacuum engine, to make room for the high-pressure 

 expansive steam-engine, with or without vacuum. 



"About 1812 Captain Trevithick threw out the Boulton and 

 Watt waggon "boilers at Dolcoath and put in his own, known as 

 Trevithick's boiler. They were about 30 feet long, 6 feet in 

 diameter, with a tube about 3 feet 6 inches in diameter going 

 through its length. There was a space of about 6 inches 

 between the bottom of the tube and the outer casing. Many 

 persons opposed the new plans. The Boulton and Watt low- 

 pressure engine did not work well with the high steam, and the 

 water rose in the mine workings. Captain Trevithick, seeing 

 that he was being swamped, received permission from the mine 

 managers to dismiss the old engine hands and employ his own 

 staff. Captain Jacob Thomas was the man chosen to put things 

 right. He never left the mine until the engine worked better 

 than ever before, and forked the water to the bottom of the 

 mine. Before that time the average duty in the county by 

 the Boulton and Watt engines was seventeen or eighteen mil- 

 lions, and in two or three years, with Trevithick's boilers arid 

 improvements in the engines, the duty rose to forty millions. 

 About 1826 he (Captain Vivian) was manager of Wheal To wan ; 

 their engines were considered the best in the county, doing 

 eighty-seven millions; they had Trevithick's boilers, working 

 with high-pressure steam and expansive gear ; few if any of 

 Boulton and Watt's boilers could then be found in the county. 

 Sir John Kennie and other scientific men, who doubted the 

 reports of the duty, came and made their own trials with the 

 engines, and were satisfied that the duty was correctly reported. 



" About that time a Mr. Neville requested him to repoH on 

 the engines at his colliery at Llanelthy; one was an atmo- 

 spheric of Newcomen's,. doing six millions ; and four or five of 

 Boulton and AVatt's patent engines averaged fourteen millions." l 



When at last the cylindrical high-pressure boiler 

 was admitted, and men had been taught to fire them, 



1 Captain Nicholas Vivian was a schoolfellow and intimate friend of Tre- 

 vithick's; he resided at Camborne in 1858, when he gave his recollections. 



