IMPORTANCE OF WINDS AND RAINS 195 



tion of winds, and cloudy, rainy, and sunlit areas are all 

 indicated. This is the kind of weather-map which is issued 

 daily by the government. Accompanied by the weather 

 forecast, such maps are posted up in post-offices and other 

 places all over the country. You will find it interesting and 

 instructive to examine and try to interpret them. 



Thunder-Storms. Have you ever watched the approach 

 of a thunder-storm ? On some hot summer afternoon you 

 may have seen dark clouds piling up in the west, and 

 rapidly approaching. They seem to hang low over the 

 earth, and to mount high in the sky, until they may fill 

 half the heavens, and it becomes as dark as twilight. Then 

 comes a gust of cool wind, followed by the first big drops. 

 It is time now to run for shelter, for the storm is about 

 to "break." Soon there comes a great downrush of rain. 

 There are dazzling flashes of lightning, and thunder like the 

 booming of many cannon. But soon the rain stops, the 

 sky clears, and the clouds, white now with the sunlight on 

 them, float away to the east. The air is cooler and the 

 whole earth seems refreshed. In the eastern sky there 

 may be a rainbow. 



; Such storms are usually quite local. They are due 

 to what may be called an "overload" of moisture in the 

 atmosphere, from which it finds relief through sudden 

 rather than through gradual means. Since the hotter 

 the air, the more moisture it absorbs, it is easy to see why 

 thunder-storms usually occur in summer, on particularly 

 hot days, more frequently by day than by night, and in 

 the afternoon more frequently than in the morning. Light- 

 ning is the passage of strong currents of electricity through 

 the atmosphere. Sometimes these currents strike down to 



