138 GENERAL SCIENCE 



quadrant of a low. By reason of the lessened pressure ex- 

 perienced in these areas as the air currents rapidly ascend 

 there is an expansion of the air and a consequent cooling of 

 it. The skies are beclouded and some of the moisture may 

 be precipitated as snow or rain. On the other hand the 

 cool dry air from the north and northwest brings clear skies 

 and bright sunshine. 



As an easterly moving area of low pressure, or cyclone, 

 approaches and passes an observer so that successively he is 

 in its eastern edge, then in its central portions, and then in 

 its western edge, a certain succession of weather changes 

 is likely to occur. Regardless of the rate of the eastward 

 movement of the storm area and the length of time required 

 for the round of changes, the order in which these changes 

 occur, and their characteristics, will be somewhat as follows: 



1. While in the eastern edge, an increasing cloudiness 

 culminating in more or less of precipitation; a rising tem- 

 perature; winds from the southeast, and south. 



2. While in the central portion, cloudiness and rain (or 

 snow) continued; little or no wind; relatively high tem- 

 perature. 



3. While in the western portion, cloudiness gives way to 

 clear skies; winds from northwest, and west; lower tem- 

 peratures (cooler). 



When the area of low pressure passes to the northward, 

 there is a typical succession of changes experienced by the 

 observer while enveloped in turn by the southeast, south, 

 and southwest portions of the storm area. These changes 

 are commonly (a) an increasing cloudiness, more or less of 

 precipitation, and a rising temperature; (b) a change of 

 wind direction from southeast through the south to the west, 

 with the skies clearing, and a lower temperature. 



When the storm area passes to the south of an observer 

 the wind directions change from easterly through the north 



