The prime cost of furnishing a complete hydraulic plant is of course considerable, and such as might perhaps appear an outlay not speedily enough recouped. In view, however, of the uncertain and oftentimes harassing conditions—not to speak of the pecuniary loss—under which the riveting department of shipbuilding work is conducted in the ordinary way, shipbuilders are constrained to acknowledge the economic advantages of the hydraulic system. Neither expense nor trouble have been spared in several yards to extend the hydraulic system into every feature where hydraulic work is practicable. The only feature now for which the machines presently in use are not available is the shell plating, and perhaps the decks, where such are entirely laid with plates. Indeed, it may fairly be said that hydraulic riveters have virtually supplanted manual riveting in nine-tenths of the structural features of a vessel. The percentage of rivets closed by machinery to the total number of rivets employed in a vessel’s structure has been computed to be about fifty per cent. In one of the yards fitted with the Tweddell system the following comprise the list of structural features for which the hydraulic riveters are daily employed:—Double bottom, including the thousands of detached pieces of plates and angles of which the bracket floor style of bottom is composed; side bars attaching frames to double bottom, frames and reverse frames, beams, stiffening bars, gunwale bars, keelsons, and keels. The shell plating, as has already been said, is about the only feature for which inventors and manufacturers of hydraulic riveters have now any serious difficulty in making provision. But many minds are exercised with the problem, and doubtless at no very distant date the present obstacles will be surmounted. One aspect of the question—and one which certain classes are apt to overlook—is that which regards the _mutual_ adaptation of means to the end desired. Shipbuilders have often under consideration the practicability of so modifying structural features and methods of work as that inventors of mechanical riveters will be met half-way in supplying the much-felt desideratum. Referring to this subject, Mr Henry H. West, chief surveyor to the Underwriters Registry for Iron Vessels, in a paper on “Riveting of Iron Ships,” read before the Institution of Naval Architects at its last meeting, said:—