In vessels of extreme proportions the method of forming shells two-ply, or of fitting all the shell plates edge to edge with outside covering-strakes over the fore-and-aft joints, has been recently revived and much improved. The system, although very expensive, has been adopted in vessels for the Anchor Line by Messrs D. & W. Henderson, Glasgow, and subsequently on even a more extensive scale by the Barrow Shipbuilding Company. * * * * * Affecting the structural character of modern ships very materially, but the result chiefly of an economy in labour, riveting by machine power has received a wonderfully extended application within recent years. Structurally, as well as commercially, the system has played a large part in the progressive movement under review. By its means the strength of united parts has been enhanced through the increase of their frictional resistance, and through the rigidity of joints, due to the more thorough filling of the rivet holes. The subject of hydraulic or machine power riveting will, however, receive fuller treatment in a subsequent chapter. * * * * * Within the past two or three years cast steel stems, stern-frames, and rudders, have been taking the place of forged iron work in ship construction. The practicability of manufacturing these of such strength and homogeneity as would meet the needs of ship construction even better than the ordinary forged work, had occurred some five or six years ago to several engaged in the steel trade. Mr J. F. Hall, of Messrs William Jessop & Sons, Limited, Sheffield, had the subject under consideration about that period, and actually made several small stern posts and rudders for steam yachts and launches. The advantages of solid and uniform steel castings over iron forgings—which, with their many weldings, so often prove inefficient when subject to any sudden shock—were even then rightly enough appreciated. It was only, however, after patents had been taken out by Messrs Cooke & Mylchreest, of Liverpool, for various devices connected with the actual fitting of such features to the ship’s structure—amongst other things the hanging of rudders without pintles or gudgeons—that the manufacture of cast steel stern-frames, rudders, &c., was seriously proceeded with.