12 



AKT. 6. S. KUSAKAIli; 



1. When the maximum amount of stress, to which the specimen 

 has just been subjected, is given, the modulus of rigidity is a 

 function of the stress actually acting upon it. 



2. When the stress acting upon it is given, the modulus of rigidity 

 is a function of the maximum amount of the stress to which the 

 specimen has just been subjected. 



Of these two, the first expresses simply that I looke's law is defec- 

 tive, while the second shows the existence of torsional hysteresis. 

 One numerical example is given in the following table to show how 

 the modulus of rigidity, even in the limiting case of a vanishingly 

 small stress, varies with the magnitude of the stress just previously 

 applied. 



Table II. 



Modulus of rigidity, takes at the state of a vanishingly Bmall BtresB. 



'The relation is also graphically shown in Fig. 1 1 IT IM. V. 



Here, it may l)i' necessary to remark that, even when Hooke's 

 law is approximately fulfilled, the factor of proportionality may 



entirely depend on its previous history. To give one instance, in 



the result of the experimenl shown in Figs. 1- and 13, 1*1. VII., 

 there is little or no objection to assuming 1 looke's law, provided each 

 series of observations, he it either in the case of an on or an off curve, 

 is considered independently from the other. Moreover, the factor of 

 proportionality lor the on-curve is nearly equal to (hat for the 

 corresponding off-curve. It, however, never remains the same for 

 t he I wo differenl series. 



