161 THE WATT AND THE TREVITHICK ENGINES. 



millions. The whole of the above are at per bushel of 93 Ibs., 

 and the whole of the accounts furnished by Mr. Lean are for 

 Trevithick's cylindrical boilers. 



" From the Dolcoath Mine books I find the following : 

 Paid for coals for the whole mine during the year 1811, 

 1150?. 15s. I0d., or per month, 931/. 14s. Id. Daring the first 

 three months of 1812 the coal averaged 1000?. per month. In 

 May of this year, 1812, Captain Trevithick is entered on the 

 books as paid 407. on account of boilers ; and in August of the 

 same year, for erecting three boilers, 105?. I think the three 

 boilers were at work in April, 1812, the month Mr. Lean gives as 

 the first reported. From April, 1812, to December, during nine 

 months, the cost of coals was 5512?. 6s., averaging 612?. 9s. fid. 

 per month. During the next year, 1813, the cost for coal was 

 7019?. 17s. 5d., or an average per month of 590?. 16s. 5d. I 

 cannot find the price paid per ton for the coal in these years, 

 but the average price during 1808 and 1815 was much alike, 

 making it probable that the price per ton during 1811, 1812, 

 and 1813, was nearly the same ; and that the saving of the above 

 300?. per month in Dolcoath was wholly on account of the 

 saving effected by Trevithick's cylindrical boilers. 



"The testimony of John Bryant, that the duty with the 

 waggon boiler was say fourteen millions, and that of Mr. Leaii, 

 giving twenty-one millions with the new Trevithick boiler, bear 

 much the same proportion as the charges for coals in the 

 respective periods above given. 



"In the year 1816 a new 76-inch single engine was erected 

 in the place of the old Boulton and Watt 63-inch double engine 

 with Trevithick's cylindrical boilers. The average duty per- 

 formed during the year 1817 was 43f millions. This same engine 

 is still at work, and her regular duty is from thirty-six to thirty- 

 eight millions. 



"lam, Sir, 



" Your most obedient servant, 



" CHAKLES THOMAS. 

 " FKANCIS TREVITHICK, Esq." 



Captain Charles Thomas, who was one of the most 

 experienced of Cornish miners, for many years the 



