Notwithstanding Watt’s fears of a falling off, the engine business still continued to prosper in Cornwall. Although the mining interests were suffering from continued depression, new mines were being opened out, for which pumping-engines were wanted; and Boulton and Watt’s continued to maintain their superiority over all others. None of their threatened rivals had yet been able to exhibit an engine in successful work; and those of the old construction had been almost completely superseded. In 1784, new engines were in course of erection at Poldice, New Poldory, Wheal Maid, Polgooth, and other mines. Almost the last of the Newcomen engines in Cornwall had been discarded at Polgooth in favour of one of Boulton and Watt’s 58-inch cylinder engines. [Illustration: POLGOOTH. [By R. P. Leitch.]] The dues paid yearly in respect of these and other engines previously erected were very considerable; Boulton estimating that, if duly paid, they would amount to about 12,000_l._ a year. There seemed, therefore, every reasonable prospect of the financial difficulties of the firm at last coming to an end. Boulton’s visit to Cornwall on this occasion was enlivened by the companionship of his wife, and her friend Miss Mynd. Towards midsummer he looked forward with anticipations of increased pleasure to the visit of his two children--his son Matt and his daughter Nancy--during their school holidays. It was a source of much regret to him, affectionate as his nature was, that the engrossing character of his business prevented him enjoying the society of his family so much as he desired. But he endeavoured to make up for it by maintaining a regular correspondence with them when absent. His letters to his children were full of playfulness, affection, and good advice. To his son at school he wrote telling him of his life in Cornwall, describing to him the house at Cosgarne, the garden and the trees he had planted in it, the pleasant rides in the neighbourhood, and the visit he had just been paying to the top of Pendennis Castle, from which he had seen about a hundred sail of ships at sea, and a boundless prospect of land and water. He proceeded to tell him of the quantity of work he did connected with the engine business, how he had no clerk to assist him, but did all the writing and drawing of plans himself: “When I have time,” said he, “I pick up curiosities in ores for the purpose of assays, for I have a laboratory here. There is nothing would so much add to my pleasure as having your assistance in making solutions, precipitates, evaporations, and crystallisations.” After giving his son some good advice as to the cultivation of his mind, as calculated to render him an intelligent and useful member of society, he proceeded to urge upon him the duty of cultivating polite manners, as a means of making himself agreeable to others, and at the same time of promoting his own comfort. “But remember,” he added, “I do not wish you