Page:Popular Science Monthly Volume 16.djvu/319

Rh other data for settling questions of climatology, and possibly of forecasting in some degree the character of coming seasons--are some of the problems of every day's life which the international charts and bulletins will serve to simplify or solve. Among these, none perhaps calls for an earlier and exacter solution than the translation of cyclones from the Asiatic waters over the forth Pacific Ocean to the Pacific slopes of the United States, and the kindred question of the transatlantic passage of American storms to western Europe. As we have already seen, so far as critical examination has been made of the Signal-Service weather-maps, more than one cyclone from the Pacific coast every month, on an average overleaps the Rocky Mountains and travels eastward, reaching the Mississippi Valley and the Lakes, with its original (perhaps ocean-born) strength. The ocean is preeminently the birthplace and habitat of storms. Thence when fully formed and densely stored with aqueous vapor--the fuel of the cyclonic engine--they assail the land-masses of the earth, and traversing them, unless in transitu, they perish for want of water, and turn to their native element. This is no less true of the Great Ocean that washes our Western shores, notwithstanding its name, than of the "stormy Atlantic." Uncomfortably near as the West Indian hurricanes approach our Atlantic seaboard, they affect but comparatively a small strip of the Eastern half of the United States, and often give us a wide berth. But the storms which invade our Pacific seaboard, from southern California to the mouth of the Columbia River, exert or expend their full force within the national limits and frequently cut their broad swaths entirely across the country. The golden key, therefore, to our continental meteorology is the adequate knowledge of the barometric depressions and associate "waves of high pressure" which roll over the continent from the westward, and in their progress dominate the weather to the north of the thirty-fifth parallel.

Off the California coast there exists, throughout the year, a permanent area or wave of high atmospheric pressure, or a vast "anti-cycione"—the diameter of which is something like one thousand miles. The barometer in this area reads 30·20 inches (see chart, p. 309). From its northern and western slopes, westerly and northwesterly wind-belts extend in an easterly direction across the Coast and Rocky Mountain range. The immense stationary anti-cyclone, from which flows off this broad belt of westerly winds, is probably due to the continental barrier arresting and accumulating the perennial equatorial current from the central zone of the Pacific Ocean; and has its counterpart in the similar area of high pressure lying in the Atlantic, off the coast of Spain and south of the Azores. The great highway therefore, along which the chief atmospheric currents move and introduce on our continent the storm-controlling and weather-producing influences, begins on the Pacific coast and traverses the country from west to east. As the Atlantic dominates the weather of Europe lying on its eastern