Mostly, however, three days of anticyclonic influence and three days of cyclonic influence with one day in between for rest, the transition period, make up a normal week of it. Let the American farmer thank his stars (and clouds) for that. For no other regions of the earth are so consistently watered and sunned all the year round as the great expanse of the North American Continent. The cyclone is that activity of the atmosphere which prevents us from suffering from an eternal drought. The cyclone is an accumulation of air which has become warmer than the air about it. This area of air usually has a central portion that is warmest of all. Since warmth expands, this air grows lighter and rises. Nature, steadfast in her grudge against a vacuum, causes the surrounding air to rush it. Since these contending currents cannot all occupy the central area at once they fall into a vast ascending spiral that spins faster and faster as it approaches the center. Imagine an inverted whirlpool. It is a replica on a much smaller scale of the great polar influx, except that the latter has a descending motion. The cyclone thus is tails to the anticyclone's heads, the reverse of the coin. Where the anti's air was cool and dry the cyclone's is warm and moist. The anti had a downward tendency and a motion, in our hemisphere, flowing outward from the apex in generous curves in the direction of clock hands. The cyclone has an upward tendency, flowing inward to the core contrariwise to clock hands. From these two great actions and reactions come all the varieties of our weather. To understand the procession of the cyclones and anticyclones across our plateaus, our mountains, our plains, and our eastern highland is to know why, and often when, it will be clear or not. To mentally visualize the splendid sweep of the elements on their transcontinental run is to glimpse grandeur in the order of things which will go far to offset the petty annoyances of fog or sleet. Ignorance may be bliss, but knowledge is preparedness. The anticyclone suggests a pyramid of cold, dry air. The cyclone suggests a shallow circular tank in leisurely whirl. But all comparisons are misleading and a caution is needed right here. For a storm is not a watering cart driven across our united skies by Jupiter Tonans Pluvius. It is NOT a receptacle from which rain drips until the supply is exhausted. A cyclone is a much more delicate operation than that. It is a process. It can renew itself and become a driving rain storm after it had all the appearance of being a sucked orange for a thousand miles.