[166] While in Cornwall in the previous year, Watt wrote long letters to his partner as to certain experimental alterations of “Beelzebub.” This was the original engine brought from Kinneil, which continued to be the subject of constant changes. “I send a drawing,” he wrote on the 4th August, 1777, “of the best scheme I can at present devise for equalising the power of Beelzebub, and obliging him to save part of his youthful strength to help him forward in his old age.... As the head of one of the levers will rise higher than the roof, a hole must be cut for it, which may after trial be covered over. If the new beam answer to be centred upon the end wall and to go out at a window, it will make the execution easy.... I long (he concluded) to have some particulars of Beelzebub’s doings, and to learn whether he has got on his jockey coat yet [_i. e._ an outer cylinder], for till that be done, you can form no idea of his perfection.” The engine continued to be the subject of repeated alterations, and was renewed, as Watt observed, like the Highlandman’s gun, in stock, lock, and barrel. After the occurrence of the above fire, we learn from Watt’s MS. Memoir of Boulton, that “Beelzebub” was replaced by a larger engine, the first on the expansive principle, afterwards known by the name of “Old Bess.” This engine continued in its place long after the career of Boulton and Watt had come to an end; and in the year 1857, the present writer saw “Old Bess” working as steadily as ever, though eighty years had passed over her head. The old engine has since found an honourable asylum in the Museum of Patents at South Kensington.