314 COMPOUND ENGINE. 



A report of the Royal Mail Steam Packet Company 

 in 1871 states, "by placing compound engines in the 

 4 Tasmania,' they had reduced the consumption of coal 

 to one-half the former quantity, doubled her capacity 

 for freight, and increased her speed." 1 Presuming 

 that the compound engines of the ' Tasmania ' are like 

 other engines known by that name, having high- 

 pressure steam in a comparatively small cylinder from 

 which it expands in a larger one, tubular boilers, 

 surface condensers, and screw-propeller, the saving 

 admitted in the ' Tasmania ' is just what Trevithick's 

 petition pointed out forty -three years ago to lessen 

 by one-half the weight, space, and fuel in marine, 

 steam-engines his opinion being founded on the ex- 

 perience of a lifetime, for as early as 1804 he wrote 

 on the question of compound engines, " I think one 

 cylinder partly filled with steam would do equally as 

 well as two cylinders;" 2 and again in 1816, describing 

 expansion, " The engine is now working with GO Ibs. 

 of steam, three-quarters of the stroke expansive, and 

 ends with the steam rather under atmosphere strong ;" 

 and in the same year worked the expansive compound 

 engine at Treskerby. 4 



1 See ' The Times,' October 26th, 3871, Half-yearly Report of the Chairman. 



2 See vol. ii., p. 131. 3 See vol. ii., p. 91. 4 See vol. ii., p. 104. 



