308 In and Around the Morteratsch Glacier : 



may be, no melting takes place without an adequate supply 

 of heat. 



The fresh piece of glacier-ice, which we imagine to have 

 been fetched from the Antrum, is a piece of the internal ice 

 of the glacier, inasmuch as it has not been exposed to the 

 direct action of sky-light. We have seen that the amount of 

 heat, small though it be, which is transmitted through the ice 

 by conduction, or which may be generated by the transforma- 

 tion of work, is sufficient to keep the internal ice of the glacier 

 always wet. But this moisture is not promiscuously diffused 

 through the mass of the ice: it is strictly localised and 

 confined to the interstitial spaces separating the individual 

 grains. When the piece of ice is exposed to the sun's rays, 

 this intergranular water, which, chemically speaking, is the 

 mot/ter-liquor of the grains, interrupts the passage of the rays 

 and acts upon them in the same way as does the water of 

 lakes or seas. It absorbs the disintegrating rays which are 

 allowed to pass by the solid crystalline ice, and these provide 

 the equivalent amount of heat in the water, which, being 

 everywhere in contact with the grain-surfaces, melts the equi- 

 valent amount of ice. A lump of ice of such size that a person 

 can carry it without difficulty, after exposure to a powerful 

 sun for from twenty to thirty minutes, appropriates out of the 

 rays passing through it sufficient heat to produce in its interior 

 so much intergranular fusion that the whole lump gets dis- 

 articulated and is resolved into its individual grains before the 

 mass itself has suffered sensible diminution of bulk. 



If we attempt to make the experiment on a warm summer 

 day when the sky is overcast with clouds, the disarticulating 

 effect produced by the diffused sky-light is insignificant, and 

 the lump of glacier-ice will melt as a whole, preserving its 

 smooth exterior surface, although the form of the individual 

 grains may be delineated, because the intergranular surfaces, 

 being in contact with relatively impure water, will melt at a 

 lower temperature. Consequently the smooth melting surface 

 of the block will always exhibit a channelled delineation of 

 the grains, although it may melt completely without falling 

 into grains. If the sky, without being completely overcast, is 



