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THOMPSON'S COAST PILOT. 111 _ thus obtained by one-third of the common interval between the eas, and the product will be the cubical contents of the space under the tonnage-deck; divide this product by one hundred, and the quotient, being the tonnage under the tonnage-deck, shall be deemed to be the register. ton- nage of the vessel, subject to the additions hereinafter mentioned. MEASUREMENT OF THE POOP AND OTHER CLOSED-IN SPACE. If there be a break, a poop, or any other permanent, closed-in space on the upper decks, on the spar deck, available for cargo or stores, or for the berthing or accommodation of passengers or. crew, the' tonnage of such space shall be ascertained as follows: ; Measure the internal mean length of such space in feet, and divide it into an even number of equal parts of which the distance asunder shall be most nearly equal to those into which the length of the tonnage-deck has been divided; measure at the middle of its height the inside breadths, name- ly, one at each end and at each of the points of division, numbering them successively, one, two, three, etc.; then to the sum of the end. breadths add four times the sum of the even numbered breadths, and twice the sum of the odd numbered breadths, except the first and last, and multiply the whole sum by one-third of the common interval between the breadths; the product will give the mean horizontal area of such space; then measure the mean height between the planks of the decks, and multiply by it the mean horizontal area; divide the product by one hundred, and the quotient shall be deemed to be the tonnage of such space, and shall be added to the ton- nage under the tonnage-decks, ascertained as aforesaid. MEASUREMENT OF THE THIRD OR SPAR-DECK. If a vessel has a third deck, or spar-deck, the tonnage of the space between it and the tonnage-deck shall be ascertained as follows: Measure in feet the inside length of the space, at the middle of its height, from the plank at the side of the stem, to the plank on the timbers at the stern, and divide the length into the same number of equal parts into which the length of the tonnage-deck is divided ; measure (also at the mid- dle of its height) the inside breadth of the space at each of the points of division, also the breadth of the stem and the breadth at the stern; number them successively, one, two, three, etc., commencing at the stem; multiply the second, and all other even numbered breadths, by four, and the third, and all the other odd numbered breadths, (except the first and last,) by two; to the sum of these products add the first and last breadths, multiply the whole sum by one-third of the common interval between the breadths, and the result will give, in superficial feet, the mean horizontal area of such space; measure the mean height between the plank of the two decks, and multiply by it the mean horizontal area, and the product will be the cubical contents of the space; divide this product by one hundred, and the quotient shall be deemed to be the tonnage of such space, and shall be add- ed to the other tonnage of the vessel, ascertained as aforesaid. And ifthe vessel has more than three decks, the tonnage of each space between decks,