388 



POPULAR SCIENCE MONTHLY. 



for the most part by clear, cool, crisp auaimn 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 tempera- 

 tures invariably accompanying the polar anti-cyclonic eddies. It must be remem- 

 bered 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 — 



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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 predis- 

 posing cause of hot waves in summer, and warm waves in winter. The anti- 

 cyclone 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) 



