An abstract of J I Thornycroft's paper presented at the summer meeting of the Institution on Naval Architects in 1894 at Southampton. Thornycroft stressed the importance of special large diameter "downcomers" on water-tube boilers. If these were omitted, there was reduced circulation and the boilers could not be safely forced to the same extent. The full text of Thornycroft's paper and the discussion that followed may be found in the Transactions of the Institution of Naval Architects, vol. 35, 1894, pp. 287-295.