630 MOTONORI MATSUYAMA 



part if the idea of McConnell and Miigge is correct. The develop- 

 ment of the planes parallel to the optic axis suggests that an ice 

 crystal has a greater tendency toward deformation parallel to the 

 optic axis than perpendicular to it. To what degree this property 

 of an ice crystal and the contact surfaces are concerned in the 

 deformation of ice is to be decided by further study. 



CONCLUSIONS 



In some specimens of ice a sharply defined elastic limit was 

 noted, though in other cases it was not so clearly shown. 



The modulus of rigidity of ice, when the crystals are perpen- 

 dicular to the axis of the test piece, is very small compared to that 

 of metals, and is about 2 X 10^ c.g.s. There is a slight indication 

 that it is greater when the shearing is parallel to the base of the 

 constituent crystals than when it is perpendicular. 



The Young's modulus is also very small compared to that of 

 metals. It is largest when the crystals are parallel to the length 

 of the test piece, and has the numerical value about 20X10^ c.g.s. 



Elastic fatigue was marked after repeated torsion. On account 

 of the fact that it was often necessary to use certain bars in suc- 

 cessive experiments during which they suffered from different 

 amounts of fatigue, it was difficult to compare the results bearing 

 on ice bars with crystals parallel and perpendicular to the length 

 of the test piece. Still there were some indications that beyond 

 the limit of elasticity the former orientation was stronger than the 

 latter against torsion. In the case of bending experiments, this 

 was clearly shown. 



The torsional deformations both by constant and by increasing 

 forces were observed and the result is shown by curves, though no 

 mathematical conclusions were made. The recovery curves 

 showed that the observation was approaching the stage where no 

 recovery would take place after removal of the force. 



When an ice bar with crystals parallel to its length was bent, 

 the bent portion showed the change of optical character, the extinc- 

 tion swinging around the curve. In each crystal when the bent 

 specimen consisted of parallel crystals horizontally across it, 

 parallel straight lines were observed. 



