358 TUBULAR BOILER, SUPERHEATING STEAM, 



In 1805, Lord Melville failed to keep his appoint- 

 ment with Trevithick, on his proposal to construct a 

 high-pressure steamboat. 1 Kennie, a pupil and friend 

 of Watt, and familiar with Trevithick's high-pressure 

 steam-dredgers on the Thames, was employed by Lord 

 Melville and the Admiralty on the Plymouth Break- 

 water, where in 1813 Trevithick proposed the use of 

 his high-pressure steam locomotive and boring engine. 2 

 In 1820 Rennie wrote to Watt, that the Admiralty had 

 at last decided upon having a steamer ; at that time 

 fifteen years had passed since Trevithick's offer to pro- 

 pel the Admiralty by steam-puffers, and ten years more 

 were to pass before they could make up their minds to 

 venture on high-pressure steam from his boilers. The 

 Steam Users' Association are equally hesitating, judging 

 from words just spoken by an engineer, the son of an 

 engineer : 



" Sir William Fairhairn said he had come to the conclusion, 

 after many years' experience, that it was in their power to 

 economize the present expenditure of fuel by a system which 

 might not be altogether in accordance with the views of the 

 members of the association or the public at large, and that was 

 to increase the pressure of steam. He would have great 

 pleasure in stating a few facts which might some day tend to 

 bring about a change, if not a new era, in the use of steam. 

 From the result of a series of experimental researches in which 

 he had been engaged for several years on the density, force, 

 and temperature of steam, he had become convinced that in 

 case we were ever to attain a large economy of fuel in the use 

 of steam, it must be at greatly-increased pressure, and at a rate 

 of expansion greatly enlarged from what it was at present. 

 Already steam users had effected a saving of one-half the coal 

 consumed by raising the pressure from 7 Ibs. and 10 Ibs. the 



1 Sec Trevithick's letter, 10th Jan., 1805, vol. i., p. 324. 



2 Ibid., vol. ii., p. 24, 



