A DROP OF WATER. 89 
a black end, that is, a north pole and a south pole 
together, then they are attracted and cling. I will 
make a triangle (A, Fig. 21) in which a black end 
and a red end always come together, and you see 
the triangle holds ^together. But now if I take off 
the lower bar and turn it (B, Fig. 21) so that two 
red ends and two black ends come together, then 
this bar actually rolls back from the others down the 
cardboard. If I were to break these bars into a 
thousand pieces, each piece would still have two 
poles, and if they were scattered about near each 
other in such a way that they were quite free to 
move, they would arrange themselves always so that 
two different poles came together. 
Now picture to yourselves that all the particles of 
those substances which form crystals have poles like 
our magnets, then you can imagine that when the 
heat which held them apart is withdrawn and the 
particles come very near together, they will arrange 
themselves according to the attraction of their poles 
and so build up regular and beautiful patterns. 
So, if we could travel up to the clouds where this 
fairy power of crystallization is at work, we should 
find the particles of water-vapour in a freezing 
atmosphere being built up into minute solid crystals 
of snow. If you go out after a snow-shower and 
search carefully, you will see that the snow-flakes are 
not mere lumps of frozen water, but beautiful six- 
pointed crystal stars, so white and pure that when we 
want to speak of anything being spotlessly white, you 
say that it is " white as snow." Some of these crystals 
are simply flat slabs with six sides, others are stars 
