Chap. VI.

FRANCE

261

In addition, there were three knees or curved pieces, 8 feet long and 8 inches square,nicely fitted, and pinned very securely with oak pins.

Within the caissoon were placed perpen-

dicularly other planks at the ends, 4 inchesin thickness, and 12 inches in width, pinnedwith great care ; between these and the angleties were five others, at equal distances apart,sustained by diagonal sheets, all securelypinned.

For closing the joints the outer edges of

Fig. 208.

SIDES OF CAISSOON,

Fig. *209. CARPENTRY OF CAISSOON.

the timbers were all chamfered, and moss of the oak was forced into them by meansof chisels with rounded edges, driven by iron hammers till it became very hard, andeffectually closed the joints. Oak laths soaked in water, an inch in width, rounded onone side and flat on the other, were nailed over the joint of moss, care being taken to drivethe nails alternately above and below the joint; this manner of caulking with mosshad been previously used with success for all the large barges which navigated the Loire.

To attach the upright sides to the bottom of the platform of the caissoon, Pe Cessart madeuse of a very simple contrifance, so that by drawing a wedge the whole might be releasedat one time. We have observed that the sides were composed of layers or courses ofsquared timbers; in the inside and outside of these were others placed perpendicularly, anddovetailed into the sides of the main timbers of the lower platform, which dovetails were socut, that they allowed the timber to be wedged home by an upright piece placed along theirsides, and at the bottom a void of 2 inches in depth was left, which, after the screw which

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Fig. 270.

CAISSOON.

S 3