Ships were then built up[12] of a series of transverse ribs, connected together by the outside planking and by the ceiling. There was no filling between the ribs. The ship's structure thus suffered severely from hogging and sagging stresses. The French tried to improve this by introducing oblique iron riders across the ceiling, or by laying the ceiling and the outside planking diagonally, while in other instances the whole was strengthened with vertical or diagonal riders; but none of these systems gave complete satisfaction. The Sepping system was introduced about 1810, and was early adopted by the Scotts. The bottom of the ship was formed into a solid mass of timber. The beams were connected with the side of the ship by thick longitudinal timbers below the knees, and by other stiffening members. A trussed frame was laid on the inside of the transverse frame in the hold of the ship, and the decks were laid diagonally. These members bound the ship in all directions, so as to resist the stresses due to the ship working in a seaway. The method of preserving the timber adopted at the beginning of the eighteenth century was to char the inner surface of the log, while the outer surface was kept wet; but this was superseded early in the century by the stoving system, which consisted in placing timber in wet sand, and subjecting it to the action of heat, for such time as was necessary to extract the residue of the sap and bring the timber to a condition of suppleness. This process continued until 1736, after which the timber itself was steamed. Copper sheathing was first employed on warships in 1761; prior to this lead had been used, but only occasionally. American shipbuilders held an important position, even in the British trade, for some time after the Declaration of Independence; but there was then developed a pronounced spirit of emulation amongst the British firms, which had a marked effect on competition in western seas. At the beginning of the nineteenth century much of the oversea work done by the Scotts was for the West Indian trade. The vessels were not often of more than 600 tons, but the firm continued steadily to develop their business. [Illustration: Plate VI. THE "LORD OF THE ISLES." (_See page 13._)] Between 1773 and 1829, the period of expansion under the second John Scott, to which we have already referred, the output was 16,800 tons.[13] This output included a succession of fine ships for the West India trade, to the order of some of the old Glasgow companies, amongst the number being Stirling, Gordon and Company; J. Campbell and Company; James Young and Company; and Muir and Fairlie. We may mention as typical ships, the _Grenada_, of 650 tons burden, and the _John Campbell_, of 446 tons, built in 1806, the first ships launched on the Clyde with all rigging in position.