"Then the Boulton and Watt waggon was taken out for Captain Trevithick's boilers, which he worked for several years. Two boilers were put in, each 18 feet long, 5 feet diameter, with an internal oval tube, he thinks, 3 feet by 2 feet 6 inches. Shortly after, another boiler of similar form was added, 22 feet long, 6 feet diameter, 4-feet tube. "He cannot say what the saving of coal was, but remembers that the duty performed by the engine with the waggon boiler was thirteen to fourteen millions. Mr. William West came to the mine as an engineer, and by paying great attention increased the duty of the Boulton and Watt engine and boiler to about fifteen millions. He does not recollect the duty the engine performed with the cylindrical boilers. "Mr. Thomas Lean, of Praze, the present reporter of mine engines in the western part of Cornwall, in answer to a note I sent to him, says he has no account of any report of Dolcoath engines for the _year 1812_, but during the month of April in that year the engines did 21-1/2 millions. During the whole of 1813 that engine was reported to average a duty of twenty-one millions. The whole of the above are at per bushel of 93 lbs., 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_l._ 15_s._ 10_d._, or per month, 931_l._ 14_s._ 7_d._ During the first three months of 1812 the coal averaged 1000_l._ per month. In May of this year, 1812, Captain Trevithick is entered on the books as paid 40_l._ on account of boilers; and in August of the same year, for erecting three boilers, 105_l._ 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_l._ 6_s._, averaging 612_l._ 9_s._ 6_d._ per month. During the next year, 1813, the cost for coal was 7019_l._ 17_s._ 5_d._, or an average per month of 590_l._ 16_s._ 5_d._ 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_l._ 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. Lean, 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.