SOME PHYSICAL PROPERTIES OF ICE 619 



The torsion curve for the case with crystals parallel to the axis 

 of the test piece was also obtained as on the other case and is 

 shown in Figure 5 by the broken line. Since the test specimens 

 for these two cases were of nearly the same dimensions, we can 

 compare the two curves with each other and consider the relative 

 ease of yielding to torsional stress. As long as the deforming force 

 remains less than 200 gm. the deformation for the former case is 

 much smaller than for the latter. After that the curve becomes very 

 flat showing that the specimen begins to yield readily. The curve 

 for the latter rod shows a discrepancy between the points B and C. 

 After that it still keeps on its steepness, becoming flatter after the 

 point D, though this is not shown in the figure. Attention must 

 be called to the fact that the observations for the former rod were 

 made after it had been used repeatedly for other tests. It is, 

 therefore, probable that this rod was already affected by the elastic 

 fatigue when the present series of observations began. Lacking 

 the knowledge how far this is the case, it is not safe to compare 

 the curves for weights of less than 200 gm. When the weight is 

 greater than this, it seems quite probable that the former rod, in 

 which the constituent crystals are lying transverse to it, is twisted 

 more easily than the latter, in which they are parallel to the length 

 of the rod. 



TORSION BY INCREASING FORCE 



Whatever may be the fundamental property of ice by which 

 the glacial motion takes place, the rate of accumulation of snow 

 must be one of the most important factors influencing that motion. 

 The corresponding study in the laboratory should be to find the 

 relation between the deformation and different rates of increase of 

 deforming force. For this purpose, a series of observations has 

 been made with the same two test rods of different orientations of 

 crystals as before. 



The observed deformations of the first rod, where the crystals 

 were arranged transverse to the rod, are shown in Figure 7. Since 

 the deformation of a plastic body under constant force increases 

 with time, it is clear that when the force increases slowly, the defor- 

 mation for the same amount of force will be greater than when the 

 force is increased rapidly. This relation is clearly shown in the 



