A Study in the Natural History of Ice 295 



distance, it is only with difficulty distinguished from a surface 

 of snow. Its whiteness is due to the same cause as is that of 

 a field of snow, namely, discontinuity in the discrete masses 

 of ice which compose the masses in both cases. The snow is 

 produced and deposited in very fine crystals which press but 

 lightly on each other and, when freshly fallen, it includes so 

 much air that a measured volume of it when melted does not 

 produce more than one-eighth or perhaps only one-tenth of 

 the volume of water. The snow-field with its dazzling white 

 surface is produced synthetically by deposition from the 

 atmosphere. The nearly equally dazzling white surface of 

 the glacier is produced analytically by the action of the sun's 

 rays on blue glacier-ice. The blue glacier-ice has been pro- 

 duced out of the snow of the snow-field by coalescence, 

 involving fusion and solidification under the control and 

 direction of the laws of crystalline conformity. It is easily 

 exposed by chipping away the outside layer at the surface of 

 the glacier. If the blue surface so obtained is exposed to the 

 sun's rays, it in a very short time shows a delicate etching, 

 the lines of which represent the outcrop of the contiguous 

 surfaces of the individual grains. These surfaces were already 

 bathed with the intergranular liquid above referred to, which, 

 by absorbing certain heat rays which are transmitted by the 

 ice of the solid grains, procures the heat which is then spent 

 in the further melting of the contiguous ice-surfaces. As the 

 liquid which bathes these surfaces contains the greater part 

 of the soluble impurities, pure ice, when in contact with it, 

 melts at a lower temperature than that at which it melts 

 when moistened with pure water. Therefore the internal 

 melting of the ice of the glacier by radiant heat proceeds by 

 the melting of the outside surface of each individual grain. 

 In this way the grains in the immediate surface layer of the 

 glacier rapidly get separated by gutters, by which the water 

 of the melted ice is drained away, leaving the individual 

 grains separated by air-spaces. These have the same optical 

 effect as those which separate the individual crystals of a 

 mass of snow ; they produce whiteness. This rough surface 

 of easily crushed grains is what enables the mountaineer to 



