RIGIDITY OF BOCKS AM» II YSTKKEslN FUNCTION. 



Table I. 



11 



Here, of the double sign, the upper or the lower must be selected 

 according as the required twist corresponds to the increasing or 

 decreasing state of the effective mass. 



Now plotting the value of y against the value of B : as is shown 

 in Fig. 9 PI. V., we see that y may be expressed as a linear function 

 of 6, so that 



where h is a constant depending on the imperfect elasticity of the 

 specimen. Numerical values of <x and h obtained from the above 

 experiments are : — - 



No. 8,. ^=00128 , Ä!=0'0817 



No. 32j. <r 2 =0-0132 , A,=C-0G19 

 The values of o x and ö" 2 which must be equal to each other, coincide 

 tolerably well within the error of observation. The difference of 

 plasticity of several rocks will be indicated by the relative values of 

 the constant //. 



THE DOUBLY INDEFINITE CHARACTER OF THE 

 MODULUS OF RIGIDITY. 



From the experiments, some of which are graphically shown in 

 Pis. IV. and VI., we may easily conclude that 



