Chemical and Physical Notes 47 



On Heard Island, during the short visit which the writer was 

 able to pay it from the " Challenger," the fall of ice from the 

 western portion was also nearly continuous. 



Since the days of Hugi and Agassiz,the intimate structure 

 of glacier-ice has been the object of much study by Conti- 

 nental and chiefly Swiss naturalists. Englishmen, though 

 they frequent glaciers as much as any other nation, have 

 generally ignored it. Tyndall, to whom we owe so much 

 of our knowledge about ice, recognised the existence of the 

 grain of the glacier, as it is called, but made no use of it in 

 his speculations with regard to the nature of the motion of 

 glaciers. As his theories are independent of this fundamental 

 feature of the constitution of glacier-ice, they must be pro 

 tanto incomplete. The colour of the surface of a glacier, so 

 dazzling in its whiteness that the inexperienced beholder is 

 apt to suppose it covered with freshly fallen snow, is due to 

 the disintegration of the compact blue glacier- ice into its 

 constituent grains under the influence of the radiation of the 

 sun. There is no more instructive or more impressive ex- 

 periment than to expose a block of compact blue ice taken 

 from the interior of the glacier to the direct rays of a powerful 

 sun. Such a block is easily obtained by penetrating into the 

 grotto, from which the glacier stream issues, to such a distance 

 that direct sky-light is shut out. Any of the blocks found 

 there will do, and it is to be brought out and exposed on 

 a rock. In twenty minutes or half an hour the block falls 

 down into a heap of irregularly shaped pieces of ice, each 

 of which is a grain and a single crystalline individual. In 

 higher latitudes or in dull weather, the power of the sun is 

 not sufficiently strong to effect this complete and striking 

 dissolution, but it loosens the block into its grains, which will 

 rattle if the block be shaken. 



The writer has analysed blocks of ice from many Swiss 

 glaciers, and weighed the individual grains. They are of all 

 weights up to a certain maximum, which varies with the 

 glacier and the part of it furnishing the ice. The largest that 

 he met with was from the Aletsch glacier, and it weighed 

 700 grams. It is the size or weight of the largest grains that 



