102 THE WATT AND THE TREV1THICK ENGINES. 



engine erected by Watt in Dolcoath Mine, under 

 Trevithick's management. Little further change was 

 made until 1799, when the globular boiler and internal 

 tube of Trevithick, jun., gave a second start to the 

 use in large engines of more expansive steam ; and 

 even this partial move was the result of years of 

 thought and practical experiment; for in 1792, when 

 twenty-one years of age, he was the elected judge on a 

 competitive trial between the Watt engine at Seal-hole, 

 patented in 1782, and Hornblower's double-cylinder 

 engine at Tin Croft. Each engine performed a duty of 

 ten millions, both of them were called expansive, while 

 in fact neither of them were so, for the pressure of the 

 steam in the boiler did not admit of it. As Lean says, 

 " As the steam used was raised but little above the 

 pressure of the atmosphere, it was found that the power 

 gained did not compensate for the inconvenience of a 

 more complicated and more expensive machine." Or, 

 as Watt said to Robert Hart, " We resolved to give up 

 the expansion of the steam until we could get men 

 that could work it," as he found it more costly than 

 profitable. Again in 1798, Trevithick's own writing 

 records his experiment in Dolcoath between the Bullan 

 Garden 45 -inch atmospheric engine and the Watt 63- 

 inch great double-acting engine, when the latter did 

 sixteen millions to ten millions by the atmospheric. At 

 that very time he was constructing his high-pressure 

 steam portable engines, and in the following year, 

 after seven years of most active experience, prompted 

 by the Watt lawsuit against Cornish engineers, he 

 in 1799 gave the beaten 45 -inch engine steam of 

 a higher pressure from the stronger globular boiler. 

 People, following the ideas of Watt, were still afraid of 

 Trevithick's plans, distinctly laid down in his letters of 



