96 ICE AND GLACIERS. 



the glacial world. There we see that minute peculiarities of 

 ice, the mere mention of which might at other times be regarded 

 as a scientific subtlety, are the causes of the most important 

 changes in glaciers ; shapeless masses of rock begin to relate- 

 their histories to the attentive observer, histories which often 

 stretch far beyond the past of the human race into the 

 obscurity of the primeval world; a peaceful, uniform, and 

 beneficent sway of enormous natural forces, where at first 

 sight only desert wastes are seen, either extended indefi- 

 nitely in cheerless, desolate solitudes, or full of wild, threat- 

 ening confusion an arena of destructive forces. And thus 

 I think I may promise that the study of the connection or 

 those phenomena of which I can now only give you a very short 

 outline will not only afford you some prosaic instruction, but 

 will make your pleasure in the magnificent scenes of the high 

 mountains more vivid, your interest deeper, and your admiration, 

 more exalted. 



Let me first of all recall to your remembrance the chief 

 features of the external appearance of the snow-fields and of 

 the glaciers ; and let me mention the accurate measurements 

 which have contributed to supplement observation, before I pass 

 to discuss the casual connection of those processes. 



The higher we ascend the mountains the colder it becomes. 

 Our atmosphere is like a warm covering spread over the earth 

 it is well-nigh entirely transparent for the luminous darting 

 rays of the sun, and allows them to pass almost without appre- 

 ciable change. But it is not equally penetrable by obscure 

 heat-rays, which, proceeding from heated terrestrial bodies,, 

 struggle to diffuse themselves into space. These are absorbed 

 by atmospheric air, especially when it is moist ; the mass of air 

 is itself heated thereby, and only radiates slowly into space the 

 heat which has been gained. The expenditure of heat is thus 

 retarded as compared with the supply, and a certain store of 

 heat is retained along the whole surface of the earth. But on 

 high mountains the protective coating of the atmosphere is far 

 thinner the radiated heat of the ground can escape thence 

 more freely into space; there, accordingly, the accumulated 



