Formerly in this weight there were 2240 pounds in a ton, and 112 pounds in a hundredweight, which was divided into four quarters of 28 pounds each. These are now called the long ton and the long hundred, and they are still the authorized weight of England, but in this country they are not used, except at the custom-houses for weighing goods imported from Great Britain, and sometimes for weighing coal, iron, and plaster. The following is the English Avoirdupois Table. Under the head of Avoirdupois, the following weights are in com 280 lb. Salt at U. S. Salt works = 1 Barrel. 1000 oz. Water = 1 Cubic foot. The origin of the term Avoir du pois is not certainly known and different theories are given to account for its adoption and use : 1. That it is from the Norman term Avoir du poids, which signifies goods or chattels of weight. 2. That it is from the old French Aver de pes, goods of weight. 3. That it is from an old French verb Averer, to verify. 4. That it is from the French Avoir du poids, to have weight. The following table shows the weight of a bushel of the commodities named in the left hand column, as fixed by statute in the States named at the top: In Pennsylvania, 85 lb. coarse, 70 lb. ground, or 62 lb. fine salt make 1 bushel, and 280 lb. = 1 bbl. Comparison of Avoirdupois, Apothecaries', and Troy Weight. 202. Long, or Linear Measure, is used in measuring distances, or anything that has length. The Unit of Measure may be 1 mile, 1 rod, 1 yard, &c. A Line has but one dimension-length. Linear measure is so called because it may be taken with a line; it includes Long Measure, Cloth Measure, and Surveyors' Linear Measure. 60 geographic miles, or } =1 degree on the Earth's Equator. Circumference of the Earth. Since the earth is not a perfect sphere, the degrees of latitude are not of equal length. Their average length, 69.16 miles, is therefore adopted. The geographic mile 1.15 statute miles, very nearly. The geographic mile is adopted by navigators on account of its convenience, 1 mile corresponding to 1 minute of arc. Cloth Measure has but one denomination, the yard, which is divided into halves, quarters, eighths, sixteenths, &c. The following also come under the head of Long Measure: 6 feet = 1 fathom (used in measuring depths at sea). = 128 fathoms 4 inches 21.888 inches = 1 hand (used in measuring height of horses). A Knot, used in measuring the speed of vessels at sea, is equal to a nautical mile. 203. Surveyors' Linear Measure is used in measuring roads, and boundaries of land. The Unit of Measure is 1 chain 66 feet. The pole ( = 25 links = 161 feet) is rarely used, chains being written as a whole number and links as a decimal. Engineers usually use a chain divided into feet, or a tape measure divided into feet and inches, or into feet and tenths and hundredths of a foot. 204. Square Measure is used in finding areas of surfaces, or of that which has length and breadth without thickness. Its Units of Measure, usually, are square surfaces, each of whose sides is a linear unit of the same name. 205. An Angle is the opening, or divergence, of two lines which meet. Thus, ANGLE B A B and A C meet at the point A, forming an angle A, or B A C. The lines A B and A C are called the sides of the angle. 206. When two lines meet so that the adjacent angles formed by them are equal, the angles are called Right Angles. And the lines are said to be perpendicular to each other. Thus, с A RIGHT ANGLE RIGHT ANGLE. B If A B and C D meet so as to make the angle A D C = the angle B D C, then these angles are right angles, and the lines A B and C D are per pendicular to each other. |