THE WATT AND THE TREVITHICK ENGINES. 183 



Watt's patent, about the year 1800, the highest duty of his 

 engines amounted to twenty millions, or more than double the 

 former duty, which may represent the economical value of the 

 improvement effected by Watt under his various patents. 



" The reported duty of Cornish pumping engines, by the con- 

 sumption of 94 Ibs. of coals, rose from an average of nineteen 

 millions and a half, and a maximum of twenty-six millions in 

 1813, to an average of sixty millions and a maximum of ninety- 

 six millions in 1843. It is necessary to bear in mind the dis- 

 tinction between the duty of a bushel of coal and 112 Ibs." 



Here, also, are the same general facts as to the duty 

 of the Watt engine, and the marked and rapid increase 

 of duty dating from Trevithick's Dolcoath engines in 

 1811 ; but the confusion and even contradictions in the 

 statements prove how little the subject was understood. 



" A rough draft, prepared by Mr. Edmonds on Trevithick's 

 return from America, dated 1828, for an application to Parlia- 

 ment for remuneration to Trevithick, says, * That this kingdom 

 is indebted to your petitioner for some of the most important 

 improvements that have been made in the steam-engine. 



" ' That the duty performed by Messrs. Boulton and Watt's 

 improved steam-engines in 1798, as appears by a statement 

 made by Davies Gilbert, Esq., and other gentlemen associated 

 for that purpose, averaged only fourteen millions and a half 

 (pounds of water lifted 1 foot high by 1 bushel of coal), 

 although a chosen engine of theirs under the most favour- 

 able circumstances lifted twenty-seven millions, which was the 

 greatest duty ever performed till your petitioner's improvements 

 were adopted, since which the greatest duty ever performed has 

 been sixty-seven millions, being much more than double the 

 former duty. That, prior to the invention of your petitioner's 

 boiler, the most striking defect observable in every steam-engine 

 was in the form of the boiler, which in shape resembled a tilted 

 waggon, the fire being applied under it, and the whole being 

 surrounded with mason work. That such shaped boilers were 

 incapable of supporting steam of a high pressure or temperature, 



