34 SNO W CR YSTALS. 



able to vegetation, on account of the salts which it con- 

 tains. Analysis, however, gave a negative result ; it 

 demonstrated the absence of these salts. Recourse was 

 then had to another hypothesis : it was supposed that the 

 air contained in snow is richer in oxygen than the free air, 

 and that to the action of this gas must be attributed its 

 fertilising property. Another error! The truth really is, 

 that snow maintains the soil which it covers at a perceptibly 

 constant temperature, and that, when thawing, it mellows 

 it by its aqueous infiltrations; so that if, before a fall of 

 snow, the earth has experienced the action of a strong frost 

 capable of killing injurious insects, all the chances will be 

 in favour of a fertile year. 



Snow forms crystals. To observe them clearly, you must 

 examine the snow which falls in very cold and dry weather. 

 It then appears to be a dust composed of little thin plates. 

 Look at the small flake which has fallen on your coat- 

 sleeve ; it is isolated ; hasten to examine it before it melts, 

 or before other flakes become amalgamated with it. What a 

 graceful star ! (Fig. 6, a). It is formed of six regular rays. 

 There are others which have only three, four, or five rays. 

 But on inspecting these more closely, you see that many 

 of these rays are broken or abortive, and that, when finally 

 analysed, each star possesses the same number of rays. 



Why are there continually six rays ? Why are there never 

 more nor fewer than this number? One might suspect in 

 nature a peculiar affection for the number six: as, for 



