Page:The American Cyclopædia (1879) Volume I.djvu/521

 ANEGADA ANEMOMETER 489 in the neighborhood, and highly esteemed for the power of keeping water cool in hot weather. The vicinity furnishes an extraor- dinary abundance of wheat, barley, oil, wine, and honey. The town contains several mon- asteries. It is supposed to be near the site of the ancient Illiturgis or Forum Julium. The capitulation of Baylen, so called from the neighboring place of that name, which was the opening of the French disasters in the Peninsu- lar war, was signed in Andujar in July, 1808, after severe fighting around the town. ANEGADA, a British West Indian island, the northernmost of the Virgin group and of the Lesser Antilles, 18 m. N. of Virgin Gorda; length 10 m., greatest breadth 4 m. It has but few inhabitants, who produce some cotton and food, and large quantities of salt from salt ponds. There is abundance of fresh water. Numerous shipwrecks occur, especially on a reef extending S. E. and S. from the E. end of the island. ANEL, Dominique, a French surgeon, born in Toulouse about 1679, died about 173Q. He acquired great fame by his invention of the probe and syringe still known by his name, and is also celebrated for his successful treat- ment of aneurism and fistula lachrymalis, upon which he published treatises. At the begin- ning of the 18th century he served as surgeon in the Austrian army, and in 1710 established himself at Genoa. ANEMOMETER (Gr. cve/zof, wind, and ptrpov, measure), an instrument for measuring the force of the wind. Attention was first given to this subject by Dr. Croune in 1667, and in- struments were contrived by him and by Wol- fius and others in the last century. These have all given place, however, to recent inventions of more perfect construction. The first at- tempts were to measure the force of the wind by its pressure upon a vertical plane, kept in position by a spring or by a weight suspended by a cord wound around a conical spiral axis, which weight the wind would raise more or less according to the degree of pressure on the vertical plane. A bag of air opening into a glass tube which was shaped like the letter U, and contained a fluid which by compression of the bag was forced down one leg and up the other, was another contrivance for the same purpose. Another form of it was to dispense with the bag and turn one extremity of the tube against the wind, expanding it to a funnel shape, so that the wind might blow directly into it and press upon the surface of the fluid. The tube was drawn out to a small diameter in the curve at the bottom, so as to check the sudden fluctuations caused by irregular blasts of wind. By means of this simple instrument, Dr. Lind, who invented it, ascertained the force of the wind at different velocities by the height of the column of water raised by it. A gentle breeze, moving at the rate of nearly four miles an hour, raises a column of water ^ of an inch, which is equivalent to a pressure of 2 ounces upon a square foot. A high wind moving 32J miles per hour raises the column 1 inch, with a pressure of nearly 5J pounds on the square foot. A column of 3 inches indicates a pressure of 15-J- pounds, and a velocity ex- ceeding 56 miles an hour. At 9 inches the wind is a violent hurricane moving 97 miles an hour, and exerting a pressure on the square foot of 46| pounds. The atmospheric pressure being a little over 2,000 pounds on the square foot, or equal to a column of water 33 feet high, the greatest force exerted by the wind is feeble in comparison with this. A more com- plicated apparatus was invented by Dr. Whew- ell, and another by Mr. Osier, both of which have been used in England at the meteoro- logical observatories and government institu- tions. Both are self-registering, and deter- mine the force of the wind by the number of revolutions of a windmill fly, the axis of which by perpetual screws and toothed wheels is connected with the registering pencil. In Whewell's instrument the windmill with its wheels and vane is on a horizontal plate, which revolves on the top of a vertical cylinder. The pencil is attached to a little block of wood or nut, through which passes a screw from the horizontal plate above to a circular rim below the cylinder, all which revolves around the cylinder as the wind changes. A straight rod also goes through the pencil block or nut, up and down which it slides as the screw turns. According as the wind blows gently or strongly, this screw turns slowly or fast, and carries the pencil down the cylinder at a pro- portional rate. Its point reaches the surface of the cylinder and marks upon it its position, and as the frame turns with the change of direction of the wind, the course of the wind is registered upon the face of the cylinder. For this pur- pose it is divided by vertical lines into 16 or 32 equal parts corresponding to the points of the compass. This instrument is deficient in not recording the time during which each wind blows, nor the times of its changes, nor its force at any particular moment. It merely gives the order of the changes, and the entire quantity that blows from each point. This is known by the vertical length of the pencil mark in each division of the cylinders corresponding to the courses. It is defective also by the friction of its machinery. Osier's instrument, constructed on similar principles, is more complicated than Whewell's. Its register is divided by lines into spaces, which represent the 24 hours of the the day, and in these spaces pencils inscribe lines, one of which indicates the direction, an- other the pressure of the wind, and a third, connected with a rain gauge, the quantity of rain which has fallen at every hour. The re- gister moves along by clockwork under the pencils, and at the meteorological observatory at Greenwich a new one is employed every day. In the royal exchange in London one of these instruments is in use with a register made to last a week. By the lines inscribed on the