WEATHER AND CLIMATE 13 



after and not before they have made some actual observations of 

 their own, however simple and even inaccurate these observations 

 may have been. We want to aim at giving them the joy of dis- 

 covery, the emotion which carried de Saussure through the hard- 

 ships of his ascent, which enables the Arctic explorer to endure the 

 tedium of the winter night. 



WIND. But we have spoken as if the air was perfectly still, 

 and this though we have already made some simple observations 

 on wind. Clearly the next point is to show that heated air expands 

 and rises, and chilled air descends. All books on heat give various 

 simple experiments to illustrate the expansion of solids, liquids, 

 and gases with heat, but though some of these will doubtless be 

 performed by the teacher, they have all the objection of an air of 

 unreality, which unfits them for the Nature Study course. At this 

 stage it is better, if possible, to confine oneself to observations which 

 can be made directly without special apparatus. Our aim is after all 

 to interpret the existing environment, not to introduce a new one. 



The adventurous child who has climbed to the top of a high 

 bookcase in a heated room knows that the air there is distinctly 

 hotter than on the floor. Some observation of this simple kind 

 may be taken as a starting-point, and the stepladder and thermo- 

 meter used to show that his impression is not imaginary. The 

 rush of warm air out to the landing when the door of a hot room is 

 opened may also be used to show that warm air tends to move, while 

 the previous experiment has shown that its tendency is to move 

 upward. 



With such observations as starting-points a good deal may be 

 done, and without borrowing tubes, coloured fluids, flasks, etc., 

 from the physical laboratory certain minor experiments may be 

 performed. A bottle half-filled with water or oil and lightly 

 corked, if put down close to the warm fire can be induced to shoot 

 out its cork. A piece of bladder also may be tied over the mouth 

 of a bottle filled with hot water in order to see how the bladder 

 is sucked in when the water cools. A whole series of trifling 

 experiments of this kind, chosen as being related as closely as 

 possible to daily life, should precede any statement as to the effect 

 of heat upon air. 



