18 ROUND THE YEAR 



of floating particles. Let us suppose that each 

 corner has gathered its quota of particles, and 

 that these have arranged themselves regularly 

 along rays pointing towards the centre of the 

 hexagon, and making angles of 60 with one 

 another. When the rays have pushed out a good 

 way from the centre they will attract very feebly 

 some of the floating particles which lie between them. 

 Secondary rays will then dart out into the midst of 

 the particles from the primary rays, making the same 

 angles as before. By a repetition of the process we 

 may get a star of any degree of complexity, and if 

 the particles of moisture are uniformly distributed, its 

 symmetry will be perfect. But if there is more 

 moisture or greater cold in one part than in 

 another, perfect symmetry will be lost. The branch- 

 ing rays will shoot, but nearly always at constant 

 angles, into the patches of moisture and avoid dry 

 places, just as the growing branches of a tree push 

 into the sunshine and avoid the shade. Sometimes, 

 however, the original direction of the rays is not quite 

 accurately preserved. Crystal joins to crystal, not in 

 straight lines, but with slight deviations. This is not 

 the case, so far as I know, with snow-crystals, but it 

 is common in hoar-frost and on the frosted pane. 

 The neighbourhood of a solid body may possibly set 

 up these disturbances. 



When we have got a central hexagon with rays 

 attached to its angles a common, but by no means 

 inevitable form, there is often a change in the angle 

 of attachment of the secondary rays. One of the 

 sides of the hexagon passes from one primary ray to 



