IN CLOUDS AND RIVERS, ICE AND GLACIERS. 



117 



Ft? 



In understanding how expansion of volume 

 may accompany tho act of crystallization. 



327. I place a number of magnets before 

 , ju. Thpy, as matter, are affected by grav- 

 ty, and, if perfectly free, they would move 



toward each other in obedience to the attrac- 

 tion of gravity. 



328. But they are not only matter, but 

 magnetic matter. They not only act upon 

 each other by the simple force of gravity, 

 but by the polar force of magnetism. Im- 

 agine them placed at a distance from each 

 other, and perfectly free to move. Gravity 

 first makes itself felt and draws them to- 

 gether. For a time the magnetic force issu- 

 ing from the poles is insensible ; but when a 

 certain nearness is attained, 1he polar force 

 comes into play. The mutually attracting 

 points close up, the mutually repellent points 

 retreat, and it is easy to see that this action 

 may produce an arrangement of the magnets 

 which requires more room. Suppose them 

 surrounded by a box which exactly incloses 

 them at the moment the polar force first 

 comes into play. It is easy to see that in ar- 

 ranging themselves subsequently the repelled 

 corners and ends of the magnets may be 

 caused to nress against the Bides of the box, 

 and even to burst ii, if the forces be suffi- 

 ciently strong. 



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 thr. 





FIG. 11. 



liquid ia being coole.l they approach each 

 other, in obedience to their general uttractioo 

 for each other. But at a certa! i point new 

 "**ces, some attractive, some repulsive, ema^ 



noting from special points of the molecules, 

 come into plav. The attracted points closa 

 up, the repelled points retreat. Thus tLo 

 molecules 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 DIKT BANDS OF THE MEII DE 

 GLACE. 



330. Pass from bright sunshine into a 

 moderately lighted room ; for a time all ap- 

 pears so dark that the objects in the room are 

 not to be clearly distinguished, Hit violent- 

 ly by the waves of light ( 3) the optic nervo 

 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 iho 

 Mer de Glace. The sun has sunk behind the 

 ridge cf 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 energy to climb tho slopes ad- 

 jacent to the Montanvert to a height of a 

 thousand feet or thereabout above the ice. 



332. We now look fairly down upon the 

 glacier, and see it less foreshortened than 

 from the Montanvert. We notice the dirt 

 overspreading its eastern side, due to the 

 crowding together of its medial moraines. 

 We see the comparatively clean surface of 

 the Glacier du Geant ; but we notice upon 

 tills surface an appearance which we have 

 not hitherto seen. It is crossed by a series 

 of gray bent bands, which follow each other 

 in "succession, from Trelaporte downward. 

 We count eighteen of theso from our present 

 position. (See sketch. Fig. 12.) 



333. These are the Dirt Bands of the Mcr 

 <le Glace ; they were first observed by Pro- 

 fessor Forbes in 18i2. 



334. They extend down theglackr further 

 than we can sec : and if we cross the valley 

 of Chamouni, r,ml climb the mountains 

 ;U the opposite side, to a point near the 

 little auberge, called La Fle'gere, we shall 

 command a view of the end cf the glacier 

 and observe the completion of the series cf 

 bands. We notice that they are confined 

 throughout to the portion of the glacier do- 

 rived from the Col du Geant. (See sketch, 

 Fig. 11.) 



335. We must trace them to their source. 

 You know how noble and complete a view 

 is obtained of the glacier and Col de Gt'*iut 

 from the Cleft Station above Trelaporte. 

 Thither we must once more climb : <uul 

 thence we can see the succession of Lands 

 stretching downward to the Montanvert, 

 and upward to the base of tho ice-casciuile 

 upon the Glacier du Ge'ant. The cascade is 

 evidently concerned in their formation. (See 

 Bketch, Fig. 13.) 



336. And how ? Simply enough. The gla- 

 cier, as we know, is broken transversely a,t the 

 summit of the ice- fall, and descends the do 



