14 THE BOOK OF NATURE STUDY 



From them we deduce the conclusion that as air gets warm it 

 takes up more space, and therefore becomes lighter, and so rises. 

 But as it moves even more easily than water does, it does not leave 

 a space when it moves, fresh air comes in to take its place. Without 

 stressing too much these theoretical facts we return continually 

 to our temperature observations, and we say to ourselves, England 

 is cool in summer because there is sea all round it, and the air is cool 

 over the sea, and in the daytime that cool air is always streaming 

 in towards the land to take the place of the warm air which is 

 continually rising. But at night, and in winter when the land is 

 cool or cold and the air over the sea not so cold, the sea helps to 

 keep us warm. At the same time we just think in passing that 

 over those vast hot plains in Asia in summer the air must always 

 be streaming out towards the distant sea, but in winter the icy 

 plains must have over them a thick mass of very cold air, while 

 we are feeling the mild air from the sea. In a Nature Study course 

 one would not wish to go much farther than this, but would leave 

 the thought, the picture, for the teacher of geography to elaborate 

 and enlarge later. But see to it that long before the child has been 

 plunged into the airy depths of monsoons and trade winds, deflec- 

 tion, and so forth, his imagination has been touched, his interest 

 aroused by contact with actual facts. Strive to make clear that 

 all this knowledge has been acquired by human beings equipped 

 with the same senses as himself. 



RELATIONS OF TEMPERATURE AND PRESSURE TO WIND. We 

 have now got to a point when we may begin to say something 

 about wind in its relation to pressure. We have learnt that air 

 is capable of very free movement, and we have suggested that when 

 it is warmed it always tends to rise and flow away, while fresh, 

 colder air comes in to take its place. We have shown also that 

 the difference between sea and land is one great cause of movements 

 in air. The school locality may even afford some detailed examples 

 of the effect of the proximity of water. Near large towns there 

 are usually areas of market gardens especially devoted to early 

 produce, selected because experience has shown that the particu- 

 lar locality is not liable to spring frosts. A good example is the 

 peninsula of the Wirral, whose crops of spring vegetables are 



