continuance of his connexion with the brass company was absorbing more of his time than he could afford to bestow upon it, he shortly withdrew from the concern,--partly also, because he was dissatisfied with what he considered the illiberal manner in which the managing committee were conducting its affairs. Another subject which occupied much of Boulton’s attention about the same time, was the improvement of engine boilers. At an early period he introduced tubes in them, through which the heated air of the furnace passed, thereby greatly increasing the heating surface and enabling steam to be raised more easily and rapidly. We find him in correspondence with Watt on the subject, while residing at Redruth in the autumn of 1780. He first suggested iron tubes; but Watt wrote, “I cannot advise iron for the tubes of boilers, but they may be thought of.”[201] Next Boulton suggested the employment of copper tubes; to which Watt replied, “I approve of what you observe about making copper flanches to the boiler pipes in future, and Ale and Cakes can easily be converted to that way whenever they put up a second boiler.” We find Boulton introducing four copper tubes 20 inches in diameter into the Wheal Busy boiler, which was 26 feet in length,--the fire passing through two of the tubes, and returning through the other two. Here, therefore, we have Boulton anticipating the invention of the tubular boiler, and clearly adopting it in practice, before the existence of the locomotive, for which it was afterwards re-invented. In fact, the multitubular boiler is but a modification and extension of Boulton’s principle, as applied by him at so early a period in the Cornish boilers. [201] Watt to Boulton, 17th October, 1780.