THE WATT AND THE TREVITHICK ENGINES. 155 



frequently mentioned, and so important in olden time, 

 now returns 70,000/. worth of tin yearly. 



Trevithick's first act on returning to Cornwall in 

 1810 was the erection of the high-pressure boilers and 

 pole vacuum engine at Wheal Prosper; at the same 

 time renewing his proposals to Dolcoath to use his 

 improved boilers, which had been broken off in 1806, 

 and to apply high-pressure steam to their low-pressure 

 Watt engine, with the same safety and profit as in 

 Wheal Prosper; the evidence was undeniable, so his 

 plans were agreed to, and in the early part of 1811 the 

 high-pressure boilers, called the Trevithick or Cornish 

 boilers, were constructed in the Dolcoath Mine under 

 his directions. 



Old John Bryant, who worked the Dolcoath large 

 engines both before and after the introduction of higher 

 pressure steam, including the Carloose or Bullan Garden 

 45-inch cylinder engine, Wheal Grons 63-inch cylinder 

 single engine, and the Watt 63-inch cylinder double, 

 with the bee-but boiler, such as Trevithick, sen., used 

 in 1775, 1 followed by the Watt waggon boiler, and 

 afterwards by the globular boiler of Trevithick, jun., 

 in 1799, 2 and still later also with the cylindrical boiler 

 of 1811, gave the following statement, when seventy- 

 four years old, to the writer : 



" In the old bee-but and the waggon boiler the steam pressure 

 in the boiler was not much ; we did not trouble about it so long 

 as the engines kept going: when the steam was too high it blew off 

 through the feed-cistern. When Captain Trevithick tried his high 

 steam in Dolcoath we hoisted up the feed-cistern as high as we 

 could; when the steam got up, it blew the water out of the cistern. 

 Captain Dick holloed out, ' Why don't you trig down the clack?' 



" The cylindrical boilers when they were first put in leaked 



1 See vol. i., p. 25. 2 See vol ii., p. 111). 



