386 COMPOUND ENGINE. 



proves the application of the principles of his patents of 

 1815 and 1831, embracing screw-propeller, direct-acting 

 engines, tubular boilers, high-pressure steam used expan- 

 sively, and condensation by cold surface preventing the 

 necessity of using salt water in the boilers. 



This engine, in outline, has a strong likeness to 

 Trevithick's engines, going back even to his first patent 

 of 1802, 1 followed by the direct-action high-pressure 

 steam yacht of 1806, 2 and again in 1808 3 by the iron 

 steamer with direct-action long-stroke cylinders, with 

 highly expansive steam and surface condensers, to which, 

 in 1815, 4 was added the patent compound expansive 

 steam pole and piston engine and screw-propeller, 

 embodying during the first fifteen years of the present 

 century, both in principle and in detail, the most 

 approved form of marine steam-engine with fewness 

 and simplicity of form of moving parts ; but compare 

 it with the Watt patent engine, and its difference 

 is obvious; no beam or parallel motion, no injection- 

 water necessitating the air-pump, no low-pressure 

 steam. The late Mr. William Wilson, of Perran 

 Foundry, son of Boulton and Watt's financial agent in 

 Cornwall, informed Mr. Henwood that he was with Mr. 

 W r att when some one stated that Mr. Trevithick was 

 working his engine with steam of 40 Ibs. on the inch ; 

 when Mr. Watt replied, " I could work my engine with 

 steam of 100 Ibs. to the inch, but I [would not] be the 

 engineman." 5 



Progressive experience, with increasing demand for 

 economy and speed, have caused the principles and the 

 details of Trevithick's steam-engines to be matters of 



1 See vol. i., p. 59. 2 See vol. i., p. 327. 



3 See vol. i., p. 336. 4 See vol. ii., p. 103. 



5 "Kenwood, Address to the Royal Institution of Cornwall, 1871. 



