The use of the telegraph in connection with the establishment of a weather bureau having stations for observation at convenient points throughout the country has contributed much to the science of meteorology. It is found that there are areas of high and low pressure existing at the same time in different parts of the country. These usually have their origin in the far northwest, and follow each other, sweeping down the eastern side of the Rocky Mountains and gradually bending easterly and from that to northeasterly by the time they reach the Atlantic coast. The areas of low pressure are called cyclones, while the areas of high pressure are called anti-cyclones. (By cyclone we do not mean those cloud funnels commonly called by that name that form at certain times of the year in certain sections of the country and produce such destruction of life and property. These storms are usually confined to a narrow strip and are short-lived. They arise undoubtedly from local conditions. A description of these tornadoes--for such is their true name--will be given in some future chapter.)
These centers of high and low pressure may be several hundred miles apart. In the area of high pressure, if it is in the winter season, the weather is unusually clear and cold, and generally clear and fairly cool at any season, and while there may be some wind it is not so strong as in the cyclone or low-pressure center. At this point it will be warmer and winds will prevail, with rain or snow, the winds varying in direction and intensity at a given point as the cyclone moves forward. In the center of these cyclones and anti-cyclones there will be a region of comparative calm, and the air is ascending at the center of the area of low pressure while it is pouring in on all sides from the area of high pressure where the air is compressed by a downward current from the upper regions.
The high-pressure or anti-cyclone system usually covers a larger area than the low-pressure system, where the air is ascending. While the air moves laterally from high to low, it does not move in a direct line. The air movement outside of the high-pressure center is usually not at a very high speed, but in northern latitudes in the direction of the hands of a clock. As it circles around it widens out spirally until it reaches the edge of a low-pressure system, when it bends in its course and moves in the other direction around this center, but constantly moving inward toward it in a spiral form and in a direction that is reverse to that of the hands of a clock. When the air current comes within the influence of a low-pressure or cyclonic system the velocity of its movement is very much accelerated until it has moved into the zone of quiet air in the center, where it is ascending.