12 THE BOOK OF NATURE STUDY 



the surface of the smooth water shines like a mirror, or like the 

 bright fireirons on the hearth, and we explain that just as the 

 water is throwing back much of the light into the air, so also it is 

 throwing back some of the heat. There are of course a good many 

 other points to be considered, but in the course of the excursion 

 we may rest content with the proof that water is colder than air 

 or soil under the same conditions, and also that it has a reflecting 

 surface which soil has not, leaving further and more difficult points 

 for indoor work. A boat on a considerable expanse of water, or 

 the memory of a journey by sea, may also enable us to add to our 

 notes that air above water is colder than air above dry ground. 



If the conditions make it possible it would be well to have the 

 observations repeated by some one at night, and the results shown 

 to the class, in order that they may formulate for themselves the 

 conclusion that the dry ground which warms so quickly with the 

 sun in the daytime, cools very quickly at night, while the water 

 cools little. Again, the repetition of the same observations in winter 

 will show that the winter conditions are similar to those obtaining 

 at night. The ground loses its summer store of heat much faster 

 than the sea or than a great mass of water, and the air above dry 

 ground therefore cools faster than air over the sea or a considerable 

 area of water. From these very simple observations, by the aid 

 of judicious questions, bring out the idea that a great mass of water 

 near a land area will tend to make it warmer in winter and cooler 

 in summer, cooler also during a summer's day and warmer at 

 night than it would otherwise be, and get the class to suggest 

 that this condition is fulfilled on an island, especially a small island, 

 which has the equalising sea within reach of all its area. Recall 

 the facts about the winter and summer climates of the plains of 

 Russia which have been already suggested, and let the class give 

 the reasons for the extremes of temperature there. 



Tell them also of the vast arid plains of Asia, far from any great 

 masses of water, and get them to realise at once the heat and the 

 cold. Tell them of the hotel-crowned Alpine hills where the sun 

 beats down through the clear, thin air all day, until the heat may 

 seem nearly intolerable in clear weather, and then explain how 

 chill the air becomes as the sun disappears and the heat is radiated 

 out into space through the thin blanket of air. But let this be 



