WEATHER AND CLIMATE 155 



tells the temperature, direction and velocity of the 

 wind, pressure, rainfall or snowfall, cloudiness, etc., 

 at the station from which the report is sent. 



These reports are then combined and placed upon 

 a map. From these maps it is then possible for an 

 expert to tell not only what the weather is, but also 

 to predict what it is likely to be. These predictions 

 are sometimes wrong, due to the fact that reports 

 from some stations may be missing or to a change in 

 the rate at which a storm is advancing. The few mis- 

 takes made, however, are almost negligible as com- 

 pared with the many correct forecasts. 



Through the services of the Weather Bureau warn- 

 ings of coming frosts, storms, and floods are made 

 which save annually not only many lives, but millions 

 of dollars' worth of property. Millions of dollars' 

 worth of fruit may be saved by these warnings of cold 

 waves sent to fruit growers. Shipping interests are 

 also .served by warnings of approaching storms. 



Explanation of a weather map. If we examine a 

 weather map (see Figure 58), we notice that there 

 are many things represented on it. Let us give our 

 attention first to the heavy black lines. These lines 

 are isobars (iso, equal; barus, heavy). All the weather 

 stations on the map which have the same barometric 

 pressure are joined by a solid line. At the end of 

 each of these lines is marked the figure which repre- 

 sents the pressure at all points on the line. These 

 lines make it possible to see very easily where the high 



