388
POPULAR SCIENCE MONTHLY.
for the most part by clear, cool, crisp autumn weather and was the first real break in the reign of warm weather since the cool wave (anti-cyclone) of the last three days of July. As can be seen on the chart, the winds disperse from the center, where the barometer is the highest, and the character of the winds and the local weather it distributes to any one place vary as the center of the anti-cyclone passes north or south of the locality. Since anti-cyclones are the seat and area of high atmospheric pressures, the barometric normal being thirty inches, in the scientific slang of the Weather Bureau they are denominated 'high areas,' or 'highs,' for short. In summer, when coming from the north, the 'highs' are the cause of the cool, and, in the winter, of cold waves, lower or low temperatures invariably accompanying the polar anti-cyclonic eddies. It must be remembered that many anti-cyclones are not so regular in character as the one charted. They are often vague in form and extent—this is also true of cyclonic eddies—
Fig. 1.
and the center may be trough-shaped instead of circular, as was the case with this one by the time it had reached the Atlantic Coast. Certain anti-cyclones that move along the southern circuit or that intrude from the tropical 'high,' as they tend to set up a vigorous circulation from the south to the north, are the predisposing cause of hot waves in summer, and warm waves in winter. The anticyclone is the most important eddy in the general circulation, but it was neither discovered nor named till long after the cyclonic circulation had been the subject of an abundant literature.
Chart No. 2.—The cyclonic eddy is the most interesting weather phenomenon the United States knows. Its sphere of influence is marked by extraordinary contrasts, particularly in between seasons. This typical cyclone, of November 24, 1858, shows how the warm southerly winds, blowing in toward the cyclone in front, push the isotherms to the north and create a warm wave (relatively)
