PRELIMINARY 3 



that while a day may be marked " cloudy " in the almanack at 

 the school, it may be " sunny " at a place only a few hundred 

 feet above. If the district does not render excursions of this 

 type possible, much can be done with pictures of drifting mountain 

 mists. Very many of the ordinary Swiss photographs of mountain 

 peaks show mists pouring over the rock edges at some point, 

 while other parts of the scene are in bright sunshine. The points 

 to aim at are the realisation that clouds may, in the first instance, 

 be compared to the steam from the kettle, the steam from the 

 locomotive, even to the vapour that arises from the morning plate 

 of porridge. Of these analogies the safest is perhaps the locomotive 

 blowing off steam, for one must be careful not to give the idea 

 that clouds are hot, and the heat of the steam from a locomotive 

 is not ordinarily felt by an observer on the ground. Second, 

 strive to make it clear that while in the daytime the sun is always 

 riding in his majesty in the heavens, the earth is ever producing 

 mantles of mist and cloud which hide him from our eyes. 



Again, make it clear by judicious questions that the clouds 

 prevent part of the heat no less than part of the light of the sun 

 from reaching us. Comparisons of very cloudy days with those 

 where the sky is covered with light drifting mist will show that 

 the amount of light and of heat absorbed by the cloud mantle 

 depends upon its thickness, and even at this early stage the days 

 of drifting mist may be used to show that clouds are not all of 

 the same height in the air. All this will help to lay the 

 foundation of a conception of the atmosphere and its load of 

 vapour. 



When, however, these simple observations have been con- 

 tinued for some time, whether in summer or in winter, we may 

 notice that although on the same day it is warmer in the sun than 

 out of it, yet often in winter the cloudy days are warmer than 

 the sunny ones. In winter the alternation of cold, clear frosty 

 weather, with little wind and some sunshine, and relatively warm, 

 windy, cloudy or wet days is so frequent that every winter will give 

 striking examples of both types. At a very early age a skating 

 schoolboy learns practically that if after a frost he is wakened at 

 night by a boisterous westerly wind, then it means that the frost 

 is gone and the ice breaking up. We thus see that if the sun is the 



