RIGIDITY OF ROCKS am» HYSTERESIS FUNCTION. . : : | 



PL VIII. 



Fin. 11. Yielding of Specimen No. 8 a under constant couple. The resisting 

 masses are different for the two curves. 

 „ 28 and 24. Recovery from the yielding. Specimen No. 4i was subjected 



to constant couple during a week'. 

 „ '27. Theoretical curve for recovery , deduced from hysteresis function. 

 PL IX. 



Fin. 15. Yielding of Specimen No. 4j under constant couples. Constant 

 couple has different values for different curves. 

 ,, 18. Theoretical curves for yielding. 

 PL X. 



FÎQS. 16 and 17. Relation between the rate of yielding and the time-element. 

 Specimen No. 4 1# Full lines arc theoretical curves. Eight straight 

 lines and hyperbolas should he drawn to correspond to all points. 

 PL XI. 



FiflS. 19-22. Yielding after a long time. Specimen No. 4j. 

 PL XII. 



fjn. 25. Effect of the elastic recovery on the cycles. The specimen, No. 3 ;i , 

 was subjected under a constant couple during 300.5 hours, and then 

 that strained state was taken as the centre of cycle. 



PL XIII. 



Fin. 20. Twisting and untwisting — no negative couple applied — of the speci- 

 men No. 3 3 . 



PL XIV. 



Fin. 28. Hysteresis function (due to the elastic yielding). 



PL XV. 



Fins. 29-33. Examples of the hysteresis due to the elastic yielding, calculated 

 from the hysteresis function by giving different values to the constant 

 involved in the function. The inclined straight line in each curve 

 shows how the curve shrinks if the yielding be disregarded. 



PL XVI. 



Fin. 34. Torsional hysteresis of a piece of sandstone. No. 3 3 . 



Pis. XVII. and XYIII. 



FiqS. 35-46. Examples of torsional hysteresis in several rocks of different 



