CLOUDS AND KIVEKS, ICE AND GLACIERS. 127 



329. Here then we have a conception which may 

 be applied to the molecules of water. They, like the 

 magnets, are acted upon by two distinct forces. For a 

 time while the liquid is being cooled they approach 

 each other, in obedience to their general attraction for 

 each other. But at a certain point new forces, some 

 attractive, some repulsive, emanating from special points 

 of the molecules, come into play. The attracted points 

 close up, the repelled points retreat. Thus the mole- 

 cules turn and rearrange themselves, demanding, as 

 they do so, more space, and overcoming all ordinary 

 resistance by the energy of their demand. This, in 

 general terms, is an explanation of the expansion of 

 water in solidifying: it would be easy to construct an 

 apparatus for its illustration, 



§ 48. The Dirt Bands of the Mer de Glace. 



330. Pass from bright sunshine into a moderately 

 lighted room ; for a time all appears so dark that the 

 objects in the room are not to be clearly distinguished. 

 Hit violently by the waves of light (§ 3) the optic nerve 

 is numbed, and requires time to recover its sensitiveness. 



331. It is for this reason that I choose the present 

 hour for a special observation on the Mer de Glace. 

 The sun has sunk behind the ridge of Charmoz, and the 

 surface of the glacier is in sober shade. The main 

 portion of our day's work is finished, but we have still 

 sufficient Anersry to climb the slopes adjacent to the 



