SNOW-FLAKES 19 



another in such a direction as to give an angle of 60 

 on its inner side (nearest to the centre) and an angle 

 of 120 on its outer side. But at 

 a distance from the centre of the 

 crystal, we more commonly find 

 the angle of 120 inside, and the 

 angle of 60 outside. The angles 

 which the more distant secondary 

 rays make are in such cases sup- 

 plementary to those of the more 

 central secondary rays. But the 

 angle of 60 is still there, though FIG. e. -Angles of !' 



and 6o' J . The second- 



itS place may be Changed. ary axes are turned in- 



J wards near the point of 



We may say that near the point intersection, and om- 



wards at a greater 



of intersection of the primaries distance. 

 the secondary rays are turned as 

 nearly towards the centre as their angle of 60 allows, 

 while at a greater distance they are turned away from 

 the centre. Why is this? The first arrangement is the 

 most compact, the other the least compact possible. 

 Near the centre there is at first an excess of moisture, 

 and here the rays will be crowded, often forming a 

 solid mass ; all turn towards the centre. As the rays 

 shoot further and further out the moisture becomes 

 less plentiful ; it was presumably less plentiful from 

 the first, and the growth of the crystal has further 

 diminished it. Now the new rays will take that 

 arrangement which spaces them most widely ; they 

 will all tuvnfrojn the centre. 



It is a good plan to draw all snow-crystals that are 

 observed. A pair of compasses and a ruler are 

 wanted. If you wish to draw a regular hexagon, 



C 2 



