in the sea-language, is the casing that part of a ship which is to be under water with fir-board of an inch thick; first laying hair and tar mixed together under the boards, and then nailing them on, in order to prevent worms from eating the ship's bottom.—Ships of war are now generally sheathed with copper; but copper sheathing is liable to be corroded by the action of salt water, and something is still wanting to effect this purpose. It is very probable that tar might answer very well.

In the Cornish mines, copper or brass pumps are often placed in the deepest parts, and are consequently exposed to the vitriolic or other mineral waters with which some of these mines abound, and which are known to have a much stronger effect on copper than sea-water. These pumps are generally about six feet long, and are screwed together, and made tight by the insertion of a ring of lead, and the joinings are afterwards tarred. One of these pumps was so much corroded as to render it unfit for use; but the spots of tar, which by accident had dropped on it, preserved the parts they covered from the action of the water. These projected in some places more than a quarter of an inch; and the joints were so far defended by the thin coat of tar, that it was as perfect as when it came from the hands of the manufacturer. If tar thus effectually defends copper from these acrimonious waters, can there remain a doubt of its preserving it from the much milder waters of the sea?