The lightning, at first only a faint glimmer, will have become more frequent and noticeable. If it is striking at a distance of fifteen miles the thunder will not be heard. As soon as the storm center, where the heaviest rain and the electrical display are taking place, gets within the fifteen-mile radius thunder will be heard to growl, and the tumbled cumulus clouds which may have lain along the horizon for hours will begin to approach. The storm will be upon you in ten minutes likely after the arc of foreboding blue and white cottony cloud has begun its charge across the sky. Light quickly fades from the heavens. The wind drops entirely. Streaks of lightning burn downward. Behind the arc stretches a curtain of uniform blue or gray. If the gray is lighter in places the rainfall will not be heavy. If the curtain is a uniform blue a heavy rain is sure. If the bow of clouds can be seen to tumble or is continuous and approaches fast the wind is certain to be severe,--may be from 30 to 60 miles an hour for the first few minutes. Sometimes a cloud of dust advancing before it demonstrates its force. This moment immediately before the storm breaks is the dramatic moment of the entire cyclone. As in a tragedy, the interest has built up to this supreme occasion, this knife thrust, from which interest recedes until clear skies show that the play is over. From 12 to 36 hours is the usual time required in winter. In summer the cyclone takes even longer to pass a given point, but the period of rainfall, in which the winter storm's amount is often surpassed, may not last fifteen minutes. First the blow, then a crash of thunder, and the rain in big drops, which lessen rapidly in size as the whole world seems involved in the vast forces of the storm center. Most of the precipitation occurs in the first fifteen minutes, sometimes in the first five. A hearty storm will deliver an inch in short order. Although the rain continues often for an hour and sometimes in the storms that are attached to a well-defined cyclonic system there will be two or three robust thunderstorms in succession, yet the first downpour is usually the torrential one and the others die away until the conditions that caused the outbreak have passed off. With the severer storms hail falls. The general condition of the air after a thunderstorm is cooler, dryer, and more invigorating than before. Ozone has been liberated, dust has been washed from the air and vegetation. The surest sign of a continuation of unsettled weather is the failure of the atmosphere to cool off. If the air remains sultry and heavy and depressing another shower is due. In such circumstances the wind will not have begun to blow with any great promise from the west.