Contents xxi 



PAGE 



Its whiteness is due to the same cause as that of a field of 

 snow, namely discontinuity in the discrete particles or masses 

 of ice of which they are composed. The snow-field is pro- 

 duced synthetically by the atmosphere ; the white surface of 

 the glacier is produced analytically by the sun's rays. The 

 internal melting of the ice of the glacier by radiant heat 

 proceeds by the melting of the outer surface of the individual 

 grain i ' 295 



If a glacier were exposed only to heat of convection, it 

 would melt with a smooth surface and its colour would be 

 blue. As the sun's rays analyse a piece of glacier-ice, 

 separating its constituent grains, so they continue the 

 analytical process on the isolated grain or crystal and 

 separate it into its constituent lamella? which are arranged 

 normally to the principal axis of the crystal. The Morteratsch 

 Grotto and the experimental use made of it . . . . 296 



Important observations made in February 1894 . . 297 



Delineation of the grains on the walls of the grotto 

 extends as far as direct skylight penetrates. 



Illustration of the state in summer. 



Granular feature in winter 298 



Hoar-frost produces etched figures of the granulation of 

 the ice, especially on the roof of the grotto .... 299 



Disintegration behind the surface of the walls. 



Usefulness of photography inside the grotto. By pro- 

 longing exposure views may be obtained of features which 

 the eye cannot detect. The stereoscopic camera is especially 

 useful in the study of the internal disarticulation of the ice, 

 and of other features 300 



Nature of the apparent stratification of the ice, which is 

 sometimes visible on glaciers 301 



Importance of studying the grotto in spring or early 

 summer ... . 302 



Improbability that a ribbon-structure extends through the 

 mass of a glacier. 



The case of a glacier which has never been exposed to 

 light . . . . . 303 



Water a protective medium. It is opaque to the rays 

 which disintegrate glacier-ice 304 



The Mergelin Lake and its icebergs. They are analogous 

 to those of the Antarctic Ocean 3S 



The granulation of glacier-ice is best studied at the 

 Mergelin Lake and in the month of July, when the sun is 

 powerful 306 



