No. 5. [from Nature, August 22, 1901, Vol. LXIV, 

 PP- 399-4QO-] 



THE SIZE OF THE ICE-GRAIN 

 IN GLACIERS 



IN referring to the size of the grain of the glacier in the 

 chapter on chemistry and physics in the Antarctic Manual, 

 I have given 700 grammes as the maximum weight which 

 I have observed. In August, 1895, I made an extended 

 study of the structure of glacier-ice, principally from the 

 Aletsch Glacier. The fragments of this glacier, which float 

 as icebergs in the Mergelin See, are exposed to the powerful 

 weathering influence of the summer sun, and are compara- 

 tively easily dissected into their constituent grains. A number 

 of blocks were so dissected in order to ascertain the weight 

 and size of the largest grains. The following weights of 

 single grains were determined: 700, 590, 450, 270, 255, 170, 

 155 and 100 grammes. It was observed that blocks of ice 

 contained grains of all sizes, which fitted each other so ex- 

 actly that, in the fresh unweathered block, the whole volume 

 was filled with ice. 



It was not then thought necessary to determine the weight 

 of the smaller grains. On revisiting the Mergelin See in the 

 latter part of July of this year (1901), I dissected several blocks 

 of ice more or less completely and weighed their constituent 

 grains. In order to effect the dissection a powerful sun is 

 requisite, and a powerful sun means a high atmospheric tem- 

 perature, under the influence of which the small grains melt 

 and disappear very quickly. All the grains in the block are 

 melting at the same time, but the smaller the grain the 

 greater is the ratio of its external surface to its mass. There- 

 fore the weights of the large grains are reduced to a less 



