Accordingly, the cyclone must travel in the direction of the strongest winds blowing into it, just as the vortex in the vessel with the eccentric orifice travelled in the direction of the quickest moving water. This is verified by a study of the synoptic charts of the Meteorological Office. The sun's heat has always been looked upon as the main source of the energy of our winds, but some account must also be taken of the effects of cold. It is well known that the mean pressure over Continental areas is high during winter and low during summer. As the sun's rays during summer give rise to the cyclonic conditions, so the cooling of the earth during winter gives rise to anti-cyclonic conditions. It is found during the winter months in several parts of the Continent that as the temperature falls the pressure rises, producing anti-cyclones over the cold area; whereas, when the temperature begins to rise, the pressure falls, and cyclones are attracted to the warming area. Small natural cyclones are often seen on dusty roads, the whirling column having a core of dusty air, and the centre of the vortex travelling along the road, tossing up the dust in a very disagreeable way to pedestrians. Sometimes such a cyclone will toss up dry leaves to a height of four or five feet. They are very common; but it is only when dust, leaves, or other light material is present that they are visible to the eye. CHAPTER XXX RAIN PHENOMENA The soft rain on a genial evening, or the heavy thunder-showers on a broiling day, are too well known to be written about. Sometimes rain is earnestly wished for, at other times it is dreaded, according to the season, seed-time or harvest. Some years, like 1826, are very deficient in rainfall, when the corn is stunted and everything is being burnt up; other years, like 1903, there is an over-supply, causing great damage to agriculture. The year 1903 will long be remembered for its continuous rainfall; it is the record year; no year comes near it for the total rainfall all over the kingdom. Rain is caused by anything that lowers the temperature of the air below the dew-point, but especially by winds. When a wind has blown over a considerable area of ocean on to the land, there is a likelihood of rain. When this wind is carried on to higher latitudes, or colder parts, there is a certainty of rain. Of course, in the latter case the rain will fall heavier on the wind side than on the lee side. For short periods, the heaviest falls or "plouts" of rain are during thunder-storms. When the raindrops fall through a broad, cold stratum of air, they are frozen into hail, the particles of which sometimes reach a large size, like stones. Of course, water-spouts now and again are of terrible violence.