322 TUBULAli BOILER, SUPERHEATING STEAM, 



worked at what seemed to be new facts, and converted 

 them into a new engine. 



We have traced how succeeding engineers tried to 

 prevent loss of heat. Trevithick took the first bold step, 

 and aiming at the same object, made the boiler the 

 steam-jacket for the cylinder, and in his patent of 1802 

 went still further and protected the boiler from external 

 cold, and thus describes it : " The steam which escapes 

 in this engine is made to circulate in the case round the 

 boiler, where it prevents the external atmosphere from 

 affecting the temperature of the included water, and 

 affords by its partial condensation a supply for the boiler 

 itself." 1 So that a quarter of a century before the date 

 of those Binner Downs experiments he had patented an 

 engine having neither cylinder nor boiler exposed to 

 the cooling atmosphere. The flues around the Binner 

 Downs cylinder were difficult of control Trevithick 

 says the piston packing had not been injured, showing 

 that observers thought it would be, and even the cylinder 

 was endangered, for the writer, who stoked those heating 

 flues, recollects the fires burning very brightly in them. 

 The ready transmission of heat through thin metal, 

 used by Trevithick in 1802 for heating feed-water, 

 and in the cellular bottom of the iron ship of 1808, 

 serving as a surface condenser, 2 and his experience in 

 181.2, that " the cold -sides of the condenser are suffi- 

 cient to work an engine a great many strokes without 

 any injection," 3 still followed up in 1828 by condensing 

 steam without the use of injection-water, led to what is 

 since known as Hall's surface condenser. 



The following letter is in the handwriting of the 



1 See patent specification, vol. i., p. 132. 



2 See vol. i., p. 335. 



3 See Trevithick's letter, 7th December, 1812, vol. ii., p. 18. 



