252 HELMHOLTZ 



gradually stretched by the motion of the mass: a process 

 quite analogous to the artificial one which we have demon- 

 strated. 



Thus to the eye of the natural philosopher the glacier, 

 with its wildly heaped ice-blocks, its desolate, stony, and 

 muddy surface, and its threatening crevasses, has become 

 a majestic stream whose peaceful and regular flow has 

 no parallel; which according to fixed and definite laws, 

 narrows, expands, is heaped up, or, broken and shattered, 

 falls down precipitous heights. If we trace it beyond its 

 termination we see its waters, uniting to a copious brook, 

 burst through its icy gate and flow away. Such a brook, on 

 emerging from the glacier, seems dirty and turbid enough, 

 for it carries away as powder the stone which the glacier 

 has ground. We are disenchanted at seeing the wondrously 

 beautiful and transparent ice converted into such muddy 

 water. But the water of the glacier streams is as pure and 

 beautiful as the ice, though its beauty is for the moment con- 

 cealed and invisible. We must search for these waters after 

 they have passed through a lake in which they have de- 

 posited this powdered stone. The Lakes of Geneva, of 

 Thun, of Lucerne, of Constance, the Lago Maggiore, the 

 Lake of Como, and the Lago di Garda are chiefly fed with 

 glacier waters; their clearness and their wonderfully beau- 

 tiful blue or blue-green colour are the delight of all 

 travellers. 



Yet, leaving aside the beauty of these waters, and consid- 

 ering only their utility, we shall have still more reason for 

 admiration. The unsightly mud which the glacier streams 

 wash away forms a highly fertile soil in the places where it 

 is deposited; for its state of mechanical division is extremely 

 fine, and it is moreover an utterly unexhausted virgin soil, 

 rich in the mineral food of plants. The fruitful layers of 

 fine loam which extend along the whole Rhine plain as far 

 as Belgium, and are known as Loess, are nothing more than 

 the dust of ancient glaciers. 



Then, again, the irrigation of a district, which is effected 

 by the snow-fields and glaciers of the mountains, is distin- 

 guished from that of other places by its comparatively 

 greater abundancy, for the moist air which is driven over 



