WEATHER AND CLIMATE 15 



determined not only by the fertile soil but also by the fact that 

 the climate is mild owing to the proximity of the two great estu- 

 aries of the Mersey and the Dee. 



On a smaller scale the same phenomenon is frequent. In the 

 vast area which supplies the market of London, and especially in 

 Kent and Surrey, it has been shown that the proximity of the 

 valley of even a small river, has a markedly ameliorating effect 

 upon the local climate. The teacher should look out for such 

 local examples, and by encouraging the reading of the thermo- 

 meter daily by different pupils in their own homes should get at 

 the fact that in the same district there are frequent minor differ- 

 ences of temperature. This done, make it clear that every minor 

 variation, every change between hill and valley, between marsh 

 and dry soil, between upland moor and fertile plain, is producing 

 little changes in pressure, and so starting movements in the air. 



But if it is true that every trifling change in the local conditions 

 is producing changes of temperature and therefore of pressure, one 

 wants to remember that it is infinitely more true when great areas 

 are considered. When we are in the depth of black winter the shops 

 are full of bright flowers. If some of these come from hothouses, 

 many others come from France or from the Channel Islands. 



In spring in most parts of Britain, strawberries from a distance 

 appear long before those of the locality are ripe. Seize facts of this 

 kind for after all to the majority of school children the shops 

 are a very important part of the environment and get the class to 

 deduce for themselves the existence of differences of temperature 

 on the surface of the globe. If the strawberries of Brittany are 

 red ripe while ours are green, the probabilities are that it is hotter 

 there than with us. But if the ground is hotter the air is warmer, 

 therefore it is lighter, and the sun on that peninsula is starting a 

 circulation of which quite possibly we are feeling the influence. 



Children from the south of England who go north to Scotland 

 for their holidays know that the days are longer in summer there 

 than in the south. If the direct experience be not available, every 

 railway station shows advertisements of cruises to see the midnight 

 sun. But if the sun shine longer in the north than in the south 

 on a summer's day, then the ground there must be still receiving 

 heat while that farther south is beginning to pour out its heat 



