THE STORY OF A SNOWFLAKE 



DO/ 



Then, in place of tiny drops of water we temperature will not permit of their re- 

 find a white sparkling rime encrusting the taining all the moisture brought from the 

 exterior of the vessel. With a magnifying sea. The excess returns to the liquid 

 glass we see that the rime is not a shapeless state, and tiny globules of water are formed 

 powdery mass, but each tiny white speck which remain suspended in the air as a 

 has taken a dehnite shape, like a six- cloud. The droplets do fall, but very 

 sided trumpet attached by the narrow slowly, and reach the earth as a drizzle, 

 end to the sides of the vessel, and the But if a wind or some other disturbance 

 mouth opening towards 

 the room. A simple ex- 

 periment which anyone 

 can perform will help us 

 to understand better the 

 operations which ha\'e 

 taken place. If a tiny 

 pinch of a soluble sub- 

 stance such as alum is 

 dropped into a tumbler 

 of water it dissolves and 

 is lost to sight. More 

 may be added with the 

 same result. But at last 

 a stage is reached when 

 no more \nll dissolve, 

 and the water is said to 

 be saturated with alum. 

 If we add more it only 

 sinks to the bottom. 

 Now warm the solution 

 and the undissolved 

 alum will disappear. 

 Like the air, its power 

 to absorb increases with 

 the temperature. If now 

 we aUow the solution to 

 cool, the excess of alum 

 \AiU return to the sohd 

 state. But we notice a 

 remarkable change. We 

 put in pieces irregular in 

 shape, they reappear as 

 crystals of regular form. ,^_ , , . , 



-Vdvertmg now to the problem which causes them to collide and coalesce mto 

 first engaged our attention, we see that the bigger drops, they faU as ram. It now 

 air receives water- vapour from ocean the temperature should fall very low and 

 and lake evaporated bv the sun's rays, the globules become too cold to remam m 



^ -'^ 



^^^^ 



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Photograph by S. H. IVrightsoit, Strcatliam Hill, S. W 



"THE FALL HAS CEASED." 



just as the fire disperses the steam mto 

 the room. Oxer the sea, especially in 

 tropical climates, so much is absorbed 

 that the atmosphere is practically satur- 

 ated. Winds blowing from the sea carry 

 inland air containing enormous quantities 

 of vapour. \Mien their progress is inter- 

 cepted by mountains they are compelled 

 to take an upward trend, and an alti- 

 tude is reached where the conditions of 



71 



the hquid state, each little sphere of water 

 will freeze into a minute crystal of ice. 

 The form it takes is not haphazard, but 

 is a clear, ghstening, hexagonal plate. 

 \\'hen dealing with the alum crystal it 

 might have been mentioned that if left in 

 a suitable solution it will continue to 

 grow. No hmit can be put to its size if 

 sufficient food is supplied. So our ice 

 crystal still has the power of extending 



