SOME PHYSICAL PROPERTIES OF ICE 



615 



most easily when the deforming force is parallel to the basal planes 

 of the constituent crystals. The present result shows the reverse 

 fact which suggests that there must be some other factor controlling 

 the deformation. • 



It is interesting to compare the values of elastic constants of 

 ice with those of other materials.^ 



Thus we see that ice has much smaller elastic constants than 

 metals and very small even compared to india rubber. For metals 

 the value of Young's modulus is generally about three times as 

 large as that of rigidity. For india rubber it is about three hundred 

 times as great. For ice, the value of Young's modulus is from 

 four to ten times as great as the rigidity, depending upon the 

 orientation of the constituent crystals. 



TORSION BY CONSTANT FORCE 



As long as it remains within the limit of perfect elasticity, the 

 deformation will little depend upon time. After that it will take 

 considerable time before the final position of equilibrium is reached 

 under a given force. For the purpose of finding the mode of 

 yielding by constant force, a circular rod of ice with crystals trans- 

 verse to it was twisted by different amount of torsional couple. 

 The rod was 20.85 cm. long and i .96 cm. in mean diameter. The 

 torsional angle was observed at various times after a certain 

 amount of weight was put on the hanging scale pan. The yielding 

 curves under different weights are given in Figure 4. 



As to the law of elastico-viscous flow of solids, Professor Michel- 

 son has published the results of his elaborate work with a formula 

 which is to be used for materials of widely different properties.^ 



' C. W. C. Kaye and T. H. Laby, Physical and Chemical Constants, p. 27. 

 ^ A. A. Michelsoii, Jour. GeoL, Vol. XXV (191 7), pp. 405-10, and Vol. XXVIII 

 (1920), pp. 18-24. 



