SOME PHYSICAL PROPERTIES OF ICE 613 



These data are, by no means, sufficient to determine the relation 

 between the temperature and the rigidity, or to compare this case 

 with the former. As a very rough approximation, however, if we 

 take the means of the first two and the last two and join the 

 points corresponding to them in the . ingure, we will see that the 

 joining line lies above the curve for the ice bar with transverse 

 crystals. This at least suggests that an ice mass will be deformed 

 more easily when it is twisted parallel to the optic axes of the 

 constituent crystals than when twisted parallel to their basal sec- 



FiG. 3. — Orientations of crystals in test specimens for bending 



tions. This result alone is not much to be relied upon. But it 

 is consistent with the results which will be described later. 



young's modulus 



Elastic behavior of a solid is determined by two independent 

 elastic constants. We have already found the value of the modulus 

 of rigidity of ice. It is desirable to find also the other, or Young's 

 modulus, which is the resistance of a wire to elongation defined as 

 the ratio of the stress to the strain. To determine this, the usual 

 method of bending was used, with two mirrors and the scale-and- 

 telescope method.^ 



The test specimens were bars of ice with rectangular cross- 

 section (Fig. 3). The component crystals were arranged either 

 {a) horizontally or {h) vertically transverse to the bar, or else 



' Poynting and Thomson, Properties of Matter, p. 100. 



