The arrows fly with the wind, and, as will be seen, almost without exception are moving towards the Low, or storm center, clearly demonstrating the effect of gravity in causing the air to flow from the several regions marked “High”, where the air is abnormally heavy, toward the Low, where the air is lighter. As the velocity of water flowing down an inclined plane depends both upon the slope of the plane and the roughness of its surface, so the velocity of the wind, as it flows along the surface of the earth towards the storm center, depends on the amount of the depression of the barometer at the center and the resistance offered by surfaces of varying degrees of roughness. =Storms and Cold Waves Simply Great Eddies in the Atmosphere.= Now picture in your mind that all the air inside the 30.2 isobar, as it flows inward, is rotating about the Low in a direction contrary to the movements of the hands of a watch, and you have a fair conception of an immense atmospheric eddy. Have you ever watched the placid waters of a deep-flowing brook and observed that where the waters encountered a projecting rock little eddies formed and went spinning down the stream? Well, our storms are somewhat similar eddies in the atmosphere, more or less perfect, that are carried along by the general easterly movement of the atmosphere in the middle latitudes of both hemispheres. But they are not deep eddies; the Low marks the center of an atmospheric circulation of vast horizontal extent as compared with its thickness or extension in a vertical direction. Thus a storm area extends from Washington, D. C., to Denver, Colorado, and yet extends upward only about six miles. The whole disk of whirling air, six miles thick and two thousand miles in diameter, is called a cyclone, or low-pressure area. It is important that a proper understanding be had of this fundamental idea, since the weather experienced from day to day depends almost wholly upon the movement of these migrating cyclones, or areas of low pressure, and the anti-cyclones, or areas of high pressure. The temperature readings are omitted from each station, but the average temperature of each quadrant of the Low is shown by the large black figures. The greatest difference in temperature is seen to be between the southeast and the northwest sections. This is due in part to the fact that in the southeast quadrant the air is drawn northward from warmer latitudes, and in the northwest quadrant it is drawn southward from colder latitudes, and to the further fact that winds blowing into the west side of a Low have a downward component of motion, and those blowing in on the front, or east side, have an upward component.