Watt's negotiations for partnership with Boulton were long and tedious. Dr. Roebuck's creditors concurred because, curiously enough, _none of them valued Watt's engine at a farthing_. Watt himself now began to despair, and his health failed; yet in 1774, when he had removed to Birmingham, he wrote to his father: "The fire-engine I have invented is now going, and answers much better than any other that has yet been made; and I expect that the invention will be very beneficial to me." A long series of experimental trials was, nevertheless, requisite before the engine could be brought to such perfection as to render it generally available to the public, and therefore profitable to its manufacturers. In January, 1775, six years of the patent had elapsed, and there seemed some probability of the remaining eight running out as fruitlessly. An application which was made for the extension of its term was unexpectedly opposed by the eloquence of Burke; but the orator and his associates failed, and the extension was accorded by Act of Parliament. The first practical employment of Watt's engines to any considerable extent was in the mining districts of Cornwall, where he himself was, in consequence, compelled to spend much of his time subsequent to 1775. Here he had to contend not only with natural obstacles in the dark abysses of deeply flooded mines, but with a rude and obstinate class of men as deeply flooded by inveterate prejudices. The result in the way of profit was not, however, satisfactory, notwithstanding the service to the mining interest was enormous. "It appears," says Watt, in 1780, "by our books, that Cornwall has hitherto eat up all the profits we have drawn from it, and all we have got by other places, and a good sum of our own money to the bargain."