320 TUBULAR BOILER, SUPERHEATING STEAM, 



Those words gave the result of Trevithick's experi- 

 ence made known to his friend during twenty years of 

 labour, 1 and yet by a seeming fatality his name is not 

 found in his friend's book. 



Sir John Rennie, who in youth had been employed 

 under Boulton and Watt at Soho, and had risen to be 

 a member of the Royal Society, came about that time 

 into Cornwall, at the request of the Admiralty, to make 

 examination into the work performed by Cornish pump- 

 ing engines, and selected Wheal Towan engine on which 

 to make special experiments. 2 The subject of Trevi- 

 thick's note was therefore at that period, and still is, a 

 matter of importance ; and his practical treatment of 

 the question is more instructive to young engineers than 

 complex rules. Arthur Woolf was at the same time 

 experimenting on steam at the Consolidated Mines, and 

 finding the want of agreement between the rules of low- 

 pressure and the practice of high-pressure engines, im- 

 puted the error to the escape of steam by the sides of 

 the piston. Trevithick disbelieved this, " because some 

 engines perform double as much as others, under the 

 same known circumstances," and advocated the observ- 

 ance of general practice to prove why high-pressure 

 engines were more economical than those of low-pres- 

 sure. Captain Grregor had placed fire-flues around the 

 steam cylinder and pipes, hoping thereby to exceed 

 the duty of the Wheal Towan engine, whose boiler, 

 cylinder, and steam-pipes were carefully clothed with a 

 thick coating of sawdust or other non-conductor of heat, 

 and lifted eighty-seven millions of pounds of water 1 foot 

 high by the heat from a bushel of coal weighing 84 Ibs. 

 This was the greatest duty that had ever been recorded 

 from a steam-engine. The Trevithick or Cornish boilers, 



1 See letter, vol. ii., p. 143. * See vol. ii., p. 185. 



