158 A YEAR IN SCIENCE 



and low pressure centers are located. The isobars 

 curve in irregular circular lines about these areas of 

 high and low pressures. We have already learned 

 that low centers are those toward which air tends to 

 move from all sides. This movement toward a low 

 pressure area constitutes a cyclone. Consequently a 

 low pressure represents a storm center. A high .pres- 

 sure on the other hand, represents an anticyclone, or 

 a region of fair clear weather. By examining weather 

 maps of several successive days it is possible to trace 

 the path of a low area as it moves along and across 

 the country. (See Figures 58 and 59.) The path of 

 the high pressure area which follows it can also be 

 traced. Arrows on the map indicate the direction of 

 the winds. Places of equal temperature are also indi- 

 cated on a weather map. They are connected by 

 dotted lines which are called isotherms. 



Questions 



1. What are the principal causes of variations in 

 the weather? 



2. Explain the differences between the terms 

 weather and climate. 



3. Explain the causes of the differences in the 

 seasons. 



4. How do you account for the fact that cloudy 

 days are cooler than days on which the sun is shining? 



5. Why is it warmer at noon than it is in the morn- 

 ing or evening? 



