Anemom'eter, an instrument for measuring the rate and pressure of the wind. There are several instruments for this purpose; the simplest and the one most used was invented in 1946 by Dr. Robinson. It consists of four hollow cups fastened to the ends of two horizontal iron rods which cross each other at right angles, and which are supported on a vertical rod which turns freely. It looks like four spokes of a wheel, at right angles to each other, each having a cup on the end to catch the wind, and the axle in which they are fitted being set up on end. This axle or rod is connected with a set of wheels, which record the number of revolutions. It was found that the cups whirl round with about a third of the velocity of the wind, and so, from the number of the revolutions, it is easy to calculate the rate of the wind. Another kind of instrument is the pressure anemometer. The best known is Osler's. A brass plate is fastened by springs to a vane in such a way that the varying pressure of the wind on the plate causes the springs to yield in corresponding degrees, and this is recorded on a moving sheet of paper by a pencil fastened to the vane; another .pencil records the changes in the direction of the wind, and usually a third pencil, guided by a rain gauge, shows the amount of rain that has fallen.
