One should gain a clear idea of the difference between the movements of the air in the cyclone and the movement of the cyclone itself, or its translation from place to place; how the wind must blow into the front of the storm in a direction partly or wholly contrary to the movement of the storm itself, and into the rear of the storm as it passes away; how the wind increases in velocity as it spirally gyrates about the center and approaches nearer and nearer the region where it must ascend; how the higher layers of air move spirally away from the center and thus cause an accumulation of air about and over the outer periphery of the Low, which in turn presses downward and impels the surface air inward. This whole complex system of motion moves eastward. Think of the sun drifting in space, while at the same time each of the planets maintains its respective orbit, and it will help one to visualize the phenomena of a migrating cyclone or anti-cyclone. [Illustration: CHART 4.—WINTER STORM, DECEMBER 15, 1893, 8 P.M. Black lines connect places having equal barometric pressure; red lines connect places having equal temperature; arrows point in direction wind is blowing; figures at end of arrows show wind velocity when it is more than light. ○ clear; ◓ partly cloudy; ● cloudy; R rain; S snow. HIGH indicates center of anti-cyclone, or high-pressure area; LOW indicates center of cyclone, or low-pressure area. Large figures show average temperature in each quadrant of cyclone. Shading shows precipitation area of last 24 hours.] Chart 4, constructed from observations taken twelve hours later, shows that the Low has moved from central Iowa since 8 A.M., and is now, at 8 P.M., central over the southern point of Lake Michigan. The shaded portion of the chart shows that rain has fallen during the past twelve hours throughout nearly the entire region covered by the cyclone. This was due to the mixing of the air as the storm progressed, to the cooling by expansion as the air ascended, to the more rapid rotation about the storm center, because of the further lowering of the barometer at the center of the disturbance since the preceding chart was made, and especially to the more humid air encountered as the storm moved eastward and came nearer to the supply of moist winds,—the Atlantic Ocean. [Illustration: CHART 5.—WINTER STORM, DECEMBER 16, 1893, 8 A.M. Black lines connect places having equal barometric pressure; red lines connect places having equal temperature; arrows point in direction wind is blowing; figures at end of arrows show wind velocity, when it is more than light. ○ clear; ◓ partly cloudy; ● cloudy; R rain; S snow. HIGH indicates center of anti-cyclone, or high-pressure area; LOW indicates center of cyclone, or low-pressure area. Large figures show average temperature in each quadrant of cyclone. Shading shows precipitation area of last 24 hours.]