62 THE BOOK OF NATURE STUDY 



there is often a short squall of wind, which precedes the approach 

 of the storm. If the storm is very distant, the cloudstmay take 

 on a peculiar anvil shape. As a general rule the severest lightning 

 occurs near the beginning of the heaviest rain. Thunderstorms 

 frequently appear in the west, and travel away towards the east. 

 As they pass away, and the clouds break, the sun shining on the 

 posterior part of the rain cloud produces a rainbow, the bow being 

 more nearly complete the nearer the sun is to the horizon. On the 

 level, rainbows are not seen in the middle of the day the sun 

 must be fairly low either in the western or the eastern sky. Their 

 association either with thunderstorms, or with those short but 

 heavy showers which resemble thunderstorms so closely, should 

 be insisted upon. They are most common in summer, or at 

 least in the warmer parts of the year, and rarely occur except after 

 short showers. Note that after long-continued rain we rarely see 

 a bow, the reason being that the sky is then usually too continuously 

 covered with cloud for the sun and a rain cloud to appear at 

 opposite points of the horizon, as is necessary for the phenomenon 

 to develop. When there are two bows, note that the second is 

 fainter than the first, and has its colours inverted as compared 

 with the first. In the case of a school placed near the sea, the 

 rainbow should be compared to the similar phenomenon often 

 visible in stormy weather, when the crests of the breakers near 

 the shore show rainbow lights. 



