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POPULAR SCIENCE MONTHLY. 



of Montana, and they follow either of two well-defined paths in 

 their eastern course. One path leads southeasterly to the Georgia 

 coast, from which locality the high follows the warm, moist air over 

 the Gulf Stream to the Gulf of St. Lawrence, there to pass beyond 

 our observation (Fig. 3). The other path extends across the Great 



Part/y C/oudy 



Cloudy 



Fig. 5. — A Newspaper Weather Map. 



Lakes and New England to the same destination. In summer the 

 larger number of highs enter our country from the Pacific Ocean 

 about the latitude of Oregon, and either pass northward along 

 the Pacific slope, whence a crossing is made over the Eockies to 

 the northern circuit from Alberta, or through the Salt Lake region 

 to the southern circuit from Alberta. Having determined the circuit 

 which a high will follow, and having found its rate of travel from 

 observation, it becomes largely a matter of calculation to foretell 

 its progress across the continent. 



While the highs have only two points of entrance to the United 

 States, the lows or storms originate in nine different districts through- 

 out the country. In Fig. 3 the heavy full lines represent the 

 paths of the highs. The lighter full lines indicate the origins 

 and paths of the lows, and the heavy dotted line is the axis or path of 

 the middle of the cold waves. It will be seen that the lows follow the 

 two circuits, northern and southern, of the highs, and that they 

 occasionally cross over from the southern to the northern circuit. 

 Some of them originate in the West Indies and travel up the Atlantic 

 coast. 



Fig. 4 shows the nine districts into which the United States has 



