SOME PHYSICAL PROPERTIES OF ICE 



617 



If we calculate the values of constants for that formula from the 

 foregoing data, we can obtain the final value of torsion for each 

 weight. Since the writer expects to obtain more detailed data 

 for ice by further experiments, he will be, for the present, satisfied 

 by finding the final positions by graphical extrapolation. The 

 relation between the torsion and the applied force, thus found, is 

 given in Figure 5. This curve is not the same as the curve in 

 Figure i, where the mode of application of force was different 

 from the present case, as were also the dimensions of the test piece. 



14 



16 



18 



o 2 4 6 8 10 i:; 



Torsion in degrees 



"Fig. 5. — Torsion curves obtained from Figures 4 and 6. Full line: for the bar 

 with crystals transverse to its longer dimension. Broken line: for the bar with 

 crystals parallel to its axis. 



Similar observations were tried on a test piece with crystals 

 parallel to the length. It was 20.95 cm. long and 1.93 cm. in 

 diameter (Fig. 6). During this test, it was noticed that the twist- 

 ing curve for 308 gm. was very close to that for 220 gm. When 

 repeated with 220 gm. once more, the deviation curve was found 

 to be much lower than the for^ner curve for the same amount of 

 force. This fact suggests that ice shows the phenomena of elastic 

 fatigue.^ It was not learned whether this occurred after repetition 

 of small deformations or after deformation of certain amount. It 

 seems likely that this phenomena appears rather abruptly instead 

 of gradually. 



' Poynting and Thomson, Properties of Matter, p. 57. 



