Mr Skinner, Observations on the Minute Structure 0/ Ice. 33 



Observations on the Minute Structure of the Surface Ice of 

 Glaciers. By S. Skinner, M.A., Christ's College. [With Plate II.] 



[Received 20 December 1900.] 



The structure of glacier ice has been the subject of much 

 discussion, and it seems to be generally admitted that at some 

 distance below the white surface of a glacier the ice is compact, 

 transparent and free from fissures through which any flow of liquid 

 can occur. Experiments in support of this are those of Huxley 1 

 who showed that there was no infiltration of coloured liquids 

 poured into cups cut in the solid ice. Helmholtz 2 has shown 

 that closed fissures can be formed in solid ice under pressure, and 

 Tyndall 3 has shown that closed cavities can be formed by the 

 action of radiant heat. 



If a block of the solid compact ice be exposed to the light and 

 heat of the solar radiation it becomes porous and with sufficient 

 exposure to intense sunlight will break up into prismatic granules 

 of various sizes. Hence above the compact ice the layer which is 

 thus exposed during summer is permeable to coloured fluids 

 which flow in the spaces between the granules. This porous layer 

 may be as much as a foot in thickness depending on the exposure 

 of the ice. The top layer of this granular portion is modified in 

 a further manner, and the experiments described in the following 

 paper had as their primary object the examination of the minute 

 structure of this first layer which forms the brilliant white surface 

 of a clean glacier. 



A convenient method of examining the superficial structure of 

 ice is that of Lohmann 4 who pours a mixture of ice-cold water 

 and plaster of Paris on the surface. In this way a cast is formed 

 which shows, in reverse, details which are difficult to make out by 

 direct examination. He has applied the method in the caverns 

 of the Hartz mountains in which ice is found during the whole 

 year, and the casts show a remarkable regularity of structure. 

 Similar casts have been obtained by the present author in the 

 Schafloch 5 , a limestone cavern north of Interlaken, and as these are 



1 Huxley, Phil. Mag., 1857, vol. xiv. p. 241. 



2 Helmholtz, Popular Lectures on Scientific Subjects, Ice and Glaciers. 



3 Tyndall, Glaciers of the Alps, p. 353. 



4 H. Lohmann, Das Hbhleneis unter besonderer Berucksichtigung einiger Eis- 

 huhlen des Erzgebirges. Jena, 1895. 



5 Two and a half hours above Merligen on Lake Thun ; 5840 feet above sea level. 



VOL. XI. PT. I. 3 



