14 ROYAI, SOCIETY OF CANADA 



The bending of a bar of ice was shown to take place by the sliding 

 of a number of layers of finite thickness. To account for the distortion 

 of the ice-bars in his experiments, McConnell was led to believe that a 

 shear or slipping of the planes took place, giving rise to the observed 

 plasticity. He proved this by obtaining the direction of the optic at is 

 of the various cr}^stals by polarized light. 



One of the most interesting features of McConnell's work is the 

 large amount of bending and recovery of ice, which was out of all pro- 

 portion to known effects in other substances. 



McConnell determined from his experiments what he called the 

 plastic coefficient, or inverse of the viscosity. He gives as a value for this 

 coefficient the number A x lO-H cm. grm.-i sec, where A lies between 

 1 and 10. 



Elasticity. 



The measurement of the elasticity of ice is a matter of some diffi- 

 culty, on account of the permanent change of form which takes place 

 under load. Using the method of bending moments, which is perhaps 

 the most convenient one, far too great values for Young's modulus are 

 obtained unless the readings are taken during the first few seconds. 

 Thus Moseley, in 1871, gives a value of 92700 in kilograms per square 

 centimetre and Bevan the value 60000 Kg/cm-. 



Making use of sounding ice plates Eeusch found the value 23632 

 kg/cm2, which was subsequently verified by the careful work of Hans 

 Hess in 1902, who made an extended study of glacier ice. His work is 

 of considerable interest and importance. He found that an ice bar cut 

 from a block, when mounted in the usual way and loaded in the middle, 

 showed a slow settling with time, after the first small deflection due to 

 bending had taken place. The slow change went on regularly with time 

 and represented the gradual shearing of the crystals. The rate of change 

 due to the shear was widely different for different loads. On removing 

 the load the bar recovered somewhat at once and then continued to re- 

 cover slowly for a few minutes. This was put down by Hess to residual 

 elasticity. 



The work of Hess was carried out on bars about 1 . 2 cm. thick, 2 . 5 

 cm. wide, and from 4 to 16 cms. long. The loads varied from 1 to 5 

 kilograms. The bars were cut with the crystalline axis parallel to the 

 width, to the length, and to the thickness. Determinations of the mo- 

 dulus showed that this varied in the proportion of 1 to 3 to 5 for the 

 cases where the principal crystalline axis was at right angles to the plane 

 of the bending force in the direction of the bending force and when the 

 plane of the axis was at right angles to the direction of bending force. 



