MEASUREMENT OF Sums FOR TONNAGE. The measurement of ships to determine their tonnage (q.v.) is now made in practically the same way by all maritime nations. The old rule in the United States was established by net of Congress in 1799. This provided that the ton nage should be ascertained as follows: From the extreme length in feet deduct three-fourths the breadth; multiply the remainder thus ob tained by the breatitli and this product by the depth; divide the last product by 95 and the quotient was the register tonnage for payment of dues. In this rule the depth of a double-decked vessel was arbitrarily assumed as one-half the breadth. so that it was to the interest of ship owners to build deep ships without much regard to the effect of the deepening upon other quali ties. Iri Great Britain a somewhat similar rule obtained. The square of the breadth was multi plied by the inboard length and the product divided by 94. This rule had the same effect on ship construction as that of the United States; and the rule is still sometimes employed in yacht and pleasure boat measurement. Ton nage so obtained is designated as 'old measure ment'; thus, 320 tons (0.M.).
In 1835, due to the efforts of Mr. Moorsom, an act of Parliament provided for a more accurate determination of the tonnage of vessels. Instead of a thumb rule which might be—and usually was—very much in error. the measurement of the cubic contents of vessels was effected in accord ance with Newton's theorem for the determina tion of contents of solids bounded by irregular surfaces. This act was followed by the 'Merchant Shipping Act of 1854,' which is the basis of the present practice throughout the maritime world, though some of its provisions have been modified in England as well as elsewhere.
The method of measuring prescribed in this act and subsequent amendments is as follows: Measure the length of the ship on the tonnage deck from the inside of the planking or plating at the extreme forward end at the stem to the inside of the planking or plating at the ex treme after end at the stern, and deduct the rake of bow and stern in the thickness of the deck so as to reduce the measurement to the length of the ship at the under side of the deck or tops of the beams. This is the 'length on the tonnage deck,' which deck is the upper one in all ships which have less than three decks and second deck from below in all others. Divide the length obtained as follows: In ships which have a length on the tonnage deck of 50 feet, this length is divided into 4 equal parts; a length of 50 to 120 feet, into 6 equal parts; 120 to 180 feet into S equal parts; 180 to 225 feet into IO equal parts; and over 225 into 12 equal parts. The division marks being established. ascertain the depth at the midship division mark: if it exceeds 16 feet divide it into 7 equal parts, if 16 feet or less. into 5 equal parts. _Measure the inside breadth of the ship at each mark and at the upper part of the depth and number them from top to bottom; multiply the 2d and 4th by 4 and the 3d by 2; add these products together and to the sum add the 1st and 5th; multiply the total by one-third the com mon interval between the breadths and this product will be deemed the transverse area of the upper part of the section. Divide the lower
breadth (between the inner bottom, or upper side of double bottom and the lower division line) into four parts by equally spaced trans verse horizontal lines; measure the breadth at the four new points and at the top of the inner bottom; and proceed as before. The sum of the two areas thus determined is the total transverse area at the point. The transverse areas at the different points (4. 6. 8, 10, or 12 in number) in the length of the ship being determined, they are to he numbered from forward (or aft. either will do), the forward one being at the extreme forward end of the measured length. and the other at its extreme after end. Multiply the sec ond and every even nurnlx•red area (except the last) by 4, and the third and every odd numbered area (except the first) by 2: add these products together, and to the sum add the' first. and last if they yield anything: multiply the sum so obtained by one-third the common interval be tween the areas and the product will be the cubic contents of the ship below the tonnage deck. ' Add to this the cubic contents of all in closed spaces above the tonnage deck including in details which are thought to conduce to greater accuracy. This act !ins been supple mented by several others, notably that of March 2, 1895, which makes the American practice almost identical with the English; indeed, the wording of the law is generally the same through out. In measuring, however, the United Stales law divides vessels into six classes according to length and the divisions in each class for meas urement of transverse areas are: In Class 1 (vessels under 50 feet length on the tonnage r deck) the length is divided into 6 equal parts; in Class 2 (vessels 50 to 100 feet long), S equal parts; in Class 3 (vessels 100 to 150 feet long), 10 equal parts; in Class 4 (vessels 150 to 200 feet long), 12 equal puts; in Class 5 (vessels 200 to 250 feet long), 14 equal parts; in ('lass 6 (vessels over 250 feet long), 16 equal parts. The method of measuring and eomputing net and gross tonnage is the sane as that al ready described.
The British system of measurement has also helm adopted by the following countries on the ,dates given: Denmark. 1807; Austria-Hungary, 1871; German•, 1873; Frame, 1873; Italy, 1873: 1 Spain, 1874; Sweden. 1875; Netherlands. 1876; •Norway, 1676; (1reeve, 1878; Russia. land, 1877; Ilaiti, 1882; Belgium. 1881; Japan. 1884. In some of these the allowanre of deduc tions, particularly that for propelling machinery, differs somewhat from the 'British rnle.
BIBLIOGRAPHY". For further information, conBibliography". For further information, con- sult: instructions to Measuring Surregors (Lon don, 1891) ; /../oyfrs Scumon's .I )moose (London, 1893) ; lt'ci•i.sed Ntatutes of the Unitcd States, Section 4153; and the Supplements to the lee riscd Statutes, also the Ntatutcs at Large for 1895. The Instructions to .11CaSuring Surregars gives all the British acts eomplete with instruc tions for carrying them into etfeet, definitions.