"Treskerby and Wheal Chance were, I believe, the only mines that paid for the use of the pole patent. Mr. John Williams, sen., of Scorrier, was purser of those mines. The agreement was that patentees should have one-fourth part of the savings of coal above twenty-six millions. The one-half of this fourth part from these two mines for some years was about 150_l._ per annum. This did not relate to the boilers; Trevithick unfortunately did not take out a patent for that improvement. The adventurers of two or three mines only had the honesty to pay 100_l._ for each mine; others made use of it without acknowledgment. "RD. EDMONDS. "PENZANCE, _12th January, 1853_." Such were the recollections of the family solicitor many years after the events had passed. The cylindrical high-pressure steam boiler and engine was really included in the patent of 1802; but frequent detail changes, consequent on size and position and local requirements, were made up to 1811, when a perfected form was arrived at, which is still in use. In principle it was unaltered and not materially different in form, but being used for larger engines, looked different. The inventor saw nothing in this difference, but the public did, and in the absence of the only man who could prove their error refused to pay on the plea of its not being patented. On his return from America he demanded 1000_l._ from each of the large Cornish mines, as a settlement in full for all benefits derived from the use of the Trevithick high-pressure steam-boiler. He had proved the weakness of the law years before, when three eminent counsel had given opinions on the 1802 patent, one of them believing the patent good, because the principle contained was new; two of them feared that similarity of details might invalidate it:[151] so he determined to apply to the Government for remuneration for benefits that might be called national. [Footnote 151: See vol. ii, p. 129.] "MR. RD. EDMONDS, "HAYLE, _December 20th, 1827_. "Sir,--I send the principal heads of what you will have to put in form to lay before the House. It is very defective; but you will be assisted by Captain Andrew Vivian, who can give dates and particulars, having been engaged with Mr. Gilbert and Captain Matthew Moyle in making out the duty performed at that time by Boulton and Watt and Hornblower's engines. He can also give you the results of the late improvements, with much more information than I can give. I saw him yesterday for this purpose; he will assist you with all his power, and will call on you at Penzance on Friday or Saturday. As I shall with pleasure pay him for his trouble, you need not fear calling on him for what assistance you need.