SCIENCE OF COMMON THINGS. 93 



How snow keeps the earth warm. Why snow is white. 



596 Does snow Jceep the earth warm f 



Yes, because it is a very bad conductor j in conse- 

 quence of which, when the earth is covered with snow, 

 its temperature very rarely descends below the freezing 

 point, even when the air is fifteen or twenty degrees 

 colder. 



59 7 Why is snow a lad conductor of heat and cold f 



Because air is confined among the crystals, and air 

 is a very bad conductor ; when, therefore, the earth is 

 covered with snow, it cannot throw off its heat by 

 radiation. 



Why is there no snow in summer-time f 



Because the heat of the air adjacent to the earth 

 melts it in its descent, and prevents it from reaching 

 the surface of the earth. 



590 Why is snow white f 



Because it is formed of an infinite number of very 

 minute crystals and prisms, which reflect all the colors 

 of the ravs of light from different points, and these 

 colors, uniting before they meet the eye, cause snow to 

 appear white. 



The same answer applies to salt, loaf-sugar, etc. 



GOO Under what circumstances does snow fall in large flakes, and when 

 in small f 



The largest flakes are formed when the air abounds 

 with vapor, and the temperature is about 32 F. ; but 

 as the moisture diminishes, and the cold increases, the 

 snow becomes finer. 



6O1 What is the snow flake composed off 



Regular and symmetrical crystals, having a great 

 diversity of forms. 



6 OS Do we see the same crystals in ice f 



They exist in ice, but are so blended together that 

 their symmetry is lost in the compact mass. 



6O3 How much more bulky is snow than water ? 



The bulk of recently-fallen snow is ten or twelve times 

 greater than that of the water obtained by melting it 



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