1888.] On the Plasticity of Glacier and other Ice. 



363 



We shall now describe the experiments on compression. An oblong 

 piece of thick plate glass was laid on the table, and on ifc were placed 

 three square blocks of ice, at the angles of an equilateral triangle 

 about 9 cm. in the side. On the ice was laid a second piece of plate 

 glass similar to the first, and pressure applied by means of a lever at 

 a point immediately over the centre of the triangle. Measurements 

 were taken with callipers of the distance between the plates at three 

 points on the edge, such that each point lay on a line through the 

 centre and one angular point of the triangle. By drawing a diagram 

 to scale, it was not difficult to deduce from these measurements the 

 yielding of each block of ice. To prevent slipping, we found it 

 necessary and sufficient to freeze a slip of paper on each end of a 

 block of ice. A maximum thermometer was placed on the table close 

 by the plates, and covered over with the same cloth, so that it 

 probably gave the temperature of the ice within a degree. The 

 horizontal section of each block was 7*5 sq. cm. in area. The fourth, 

 fifth, and sixth columns give the actual contraction of the blocks 

 during each interval. They are correct probably within 0*02 mm. 

 Each measurement with the callipers was repeated, and the two 

 readings seldom differed more than 0'02 mm. 



Pressure had been applied for one day previous to those here given, 

 but owing to an accident, its magnitude was rather uncertain. The 

 remarkable difference between the plasticity of three specimens 

 of glacier ice is well shown, though in this case all three pieces 

 were from the same lump. After the experiment they were examined 

 under the polariscope. All three were composed of smallish grains 

 averaging perhaps 7 mm. in diameter. The increase of plasticity for 

 a rise in temperature from —6° to —3° is very striking in all three 

 pieces. 



Experiment No. 2 on Compression. — In this three pieces of lake ice 

 were arranged as in the last experiment. The crystalline columns 

 were vertical, so that the pressure was applied in a direction parallel 

 to them. The horizontal section of each piece was 7 sq. cm. The 

 fourth, fifth, and sixth columns of the table give the contractions 

 during each interval, calculated from the readings actually taken, as 

 explained in the description of the last experiment. They are pro- 

 bably accurate to 0"02 mm. It may be mentioned that the totals are 

 calculated to an extra place of decimals, which explains the slight 

 discrepancy observable. 



VOL. xliv. 



