MODULUS OF ELASTICITY OF ROCKS. 15 



The phenomenon of yielding, though it is not so enormous as 

 in the case of torsion, is still sufficiently great to be dealt with. 

 For a piece of sandstone, e.g., wliich was loaded with Mo = 3oOO 

 and M =3000 gramsweight, the amount of bending increased, in 

 the course of two and a half days, to, at least, more than three 

 times its initial value. It is, indeed, questionable whether there 

 is any limit to the yielding. 



Also the amount of residual surviving the bending force does 

 not I'emain constant, but recovers gradually and uninterruptedly. 

 The amount of recovery, in the case of the above specimen just 

 referred to, increased, in the course of about four days, by more 

 than twice its initial value. 



The yielding of specimens under a constant force having 

 become comparatively small after a few days, the temperature- 

 variation of the flexure may be clearly observed. The relation 

 between temperature and bending for a piece of sandstone is given 

 in Fig. 11. The curve, as a whole, expresses the simple propor- 

 tionality between the two elements. We find, however, the amount 

 of flexure has a minimum value in the neighbourhood of about 

 9°C. In the case of the rigidity-modulus, we had a result strictly 

 analogous of this effect. It may be, however, the effect of moisture. 

 To determine any general relation between elasticity and tempera- 

 ture requires further investigation by a special arrangement. 



SOME INFERENCES RELATING TO SEISMOLOGY. 



In the author's publications above cited, it was experimentally 

 as well as theoretically explained that, in the case of distorsional 

 waves, the velocity of propagation is a function of the amplitude 



