Anemography

[Gr. anemos, wind, and graphe, description.] ( Phys.) The description of the winds. Anemology, n. [Gr. anemos, wind, and logos, discourse.] (Phys.) The doctrine of, or a treatise on the winds. Anemometer, n. [Gr. anemos, wind, and metron, measure.] ( Phys.) An instrument used for measuring the force and velocity of the wind. Various instruments have been invented for this purpose, the first of which is attributed to Wolfius, who described it in 1709. Considerable improvements have been since made upon the construction of anemome ters; neverthele , that invented by Lind in 1775 (Fig. 124) is still considered to be one of the most convenient and accurate. It consists of two upright gla tubes, A B and CD, about 9 inches high, and of an inch wide, connected below by a much narrower tube, E, varying from to of an inch in width. The tube A B is bent at right angles, so as to receive the wind blowing into it horizontally. A scale, graduated in inches and parts of an inch, is placed between the tubes, and the whole instrument is made to turn round the steel spindle, G, which can be screwed into a block of wood by a screw at the bottom. When the instrument is used, water is poured into the tubes until the level in both stands at the middle of the scale. When no disturbing force acts C IMG:content-0227.png:[ocr errors] Fig . 124. upon either column of liquid, the level of both is accurately the same; but when the mouth of the tube A B is turned toward the wind, the column in A B is pre ed downward, and that in CD rises proportionably, and the difference of the heights of the two columns gives the column of water which the force of the wind sustains. Now, as we know that the pre ure of the atmosphere at the earth's surface supports a column of water about 33 feet high, or pre es with a force of about 2,060 lbs. on the square foot, this instrument gives us immediately the data from which we can calculate the pre ure or force of the wind. Thus, supposing the wind to blow with a force sufficient to raise the one column one inch above the other, we have of of 2060, or about 50 lbs. of pre ure on the square foot as the force of the wind. 10