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 of the system of diagonally bracing and trussing the frame-timbers, an invention of the first importance in shipbuilding. Hitherto, ships of the first class had suffered from the arching of their keels, technically called ‘hogging.’ This arose from the irregularity of the weight occasioned by greater upward pressure in the centre than in the extremities. When a first-rate ship entered the sea, she was usually found to have dropped two to five or six inches at head and stern. To prevent this result Seppings suggested that the frame-timbers should not, as had previously been done, be merely placed square and rectangular to each other, but that they should be braced together by trusses laid diagonally, and forming a series of triangles. While at Plymouth in 1800 Seppings had experimented in this direction on the Glenmore, an old and weak vessel of 36 guns. His success induced him, on his promotion to Chatham, to extend his operations in 1805 to the Kent, 74 guns, when docked for repairs. The plan answered all his expectations, and in 1810 it was applied with excellent effect to the old Tremendous (74). The Howe, launched on 28 March 1815, was the first ship laid down and wholly built on the diagonal principle. The system met with bitter opposition from the older shipwrights; it was pronounced to be ‘without sense or science,’ but Sir [q. v.], second secretary of the admiralty, regarded it with favour and described its merits in an article in the ‘Quarterly Review.’ Barrow induced Charles Yorke, first lord of the admiralty, to direct its adoption in the government shipyards. Seppings fully and clearly explained the new system in a paper read before the Royal Society on 10 March 1814, and supplied a print of a section indicating the arrangements in detail. He showed how a barred gate was stiffened by fixing across it a diagonal strip of wood, and proved that the diagonal braces and trusses placed on either side of the ship, with cross-bracing between the port-holes, and the attachment of the beams to the sides of the vessel by small timbers, rendered the ship one mass, and attained the essential qualities of ‘strength, safety, and durability.’ In conclusion, Seppings acknowledged the honourable spirit of liberality which dictated ‘the orders for carrying out this new principle of constructing his majesty's ships.’ A second paper, read before the Royal Society on 27 Nov. 1817 (Transactions, 1818), showed the success of the principle on its trial on the Howe (120), the St. Vincent (120), and the Justitia (74), an old Danish ship. Critics of ‘high mathematical talents, who generally approved of the system’ (, Principles, &c., p. 12), controverted some of its details; but Seppings, who had no mathematical training, proved them in the wrong by actual experiment.

A third invention by Seppings was suggested by the loss of life on the Victory (100) at the battle of Trafalgar, owing to shot passing unimpeded through the boarding of the beakhead. In 1807 Seppings recommended the replacement of the beakhead of the ship by timbers run up the sides forming a circular bow. Subsequently he introduced a round stern, which became a formidable battery.

On 14 June 1813 Seppings was appointed by patent (Admiralty Bill Office Registry of Salaries) to the office of surveyor of the navy, and was elected a fellow of the Royal Society on 10 March 1814. He received the honour of knighthood on 17 Aug. 1819 on board the Royal George yacht ‘under sail, the royal standard flying’ (Heralds' College). He received many other marks of honour at home and abroad. The Emperor Alexander of Russia, the kings of Denmark and Holland, all presented him with valuable gifts to mark their appreciation of his professional services. In 1836 the university of Oxford conferred on him the degree of D.C.L.

When, in 1832, Sir [q. v.], first lord of the admiralty, began a reform of the naval administration, Seppings resigned, on 12 June 1832, after nearly fifty years' service, his successor, Sir William Symonds, being appointed by warrant on 13 June 1832. After his retirement from Chatham, Seppings settled at Taunton, Somerset, where he died on 25 Sept. 1840. A small tablet in the chancel of St. Mary's there is inscribed with a brief record of his career.

By his innovations Seppings rendered ships in every way more seaworthy and better adapted for defence. In the museum of the Royal United Service Institution there is a fine model of a vessel presented by Seppings to the board of admiralty, which opens lengthwise, showing in opposite sections the two halves of a ship, the one with the old construction, the other with Seppings's improvements and inventions. His improved methods of shipbuilding are now universally adopted in all ships, whether constructed for the navy or the merchant service. In 1891, at the Naval Exhibition at Chelsea, the gallery in which models illustrating the progress of naval architecture were shown, was entitled the ‘Seppings’ gallery.

Lady Seppings died at Taunton on 22 Nov. 1834. Seppings's eldest son, John Milligen Seppings, filled for twenty years the office of