Figure 14 gives an illustration of what would be the movement of air inward to a cyclone on a non-rotating earth. The winds would blow along radial lines for a time, but, converging together as they began to ascend, they doubtless would soon set up a gyration about the center. On a non-rotating earth this gyration would be clockwise as often as it would be anti-clockwise, but on a rotating earth the gyration can be in but one direction. (Figure 15.) Even tornadoes, whose diameters of rotation are never but a few hundred feet, obey this law. In little dust whirls, in which the movements of air may be comprehended from the motion of the trash that is whirled about and which are tornadoes in miniature, the direction of gyration may be either way. They are too small for the deflecting force to be appreciable, and it may be that the tornado is forced to take its direction of gyration from the cyclone in whose southeast quarter it has its origin. [Illustration: FIG. 15.—Deflection of wind due to earth’s rotation.] =How Wind Velocity Increases with Altitude.= Figure 16 shows how the velocity of the wind increases with elevation in the free air up to five thousand meters (about three miles). The average for the year, for the summer and for the winter, is given. It increases most rapidly up to six hundred meters in summer and up to eight hundred meters in winter. From these two heights there is a steady and pronounced slowing down of the wind up to one thousand meters; after which it increases up to five thousand meters, and how far beyond we know not. In winter there is a singular acceleration of velocity in the stratum between two thousand and twenty-five hundred meters and then no increase for the next five hundred meters; after which there is a uniform and steady gain up to five thousand meters. Starting at two hundred and seventy meters, the average velocity for the year is 3½ meters per second, or about 7¼ miles per hour. At five thousand meters altitude the average for the year is 11¼ meters per second, or about 27 miles per hour. [Illustration: FIG. 16.—Annual, summer, and winter wind velocities, with altitude. 1, 1850 feet; 2, 2467 feet; 3, 3083 feet; 4, 15,417 feet.] CHAPTER IX HOW TO FORECAST FROM THE DAILY WEATHER MAP IT IS NOT DIFFICULT TO BECOME WEATHERWISE AND THEREBY TO GAIN ADVANTAGES IN HEALTH, HAPPINESS, AND BUSINESS