KINETIC MEASUREMENT OF THE ELASTICITY OF ROCKS. 23 



the moduli of elasticity are comparatively small Inve also a posi- 

 tive percentage, but some of them having large moduli may have 

 negative percentages. The following table vvill show the facts 

 more clearly. 



Here it must be noted that I do not mean to say that the 

 percentage would be always negative for any old rock having a 

 distinctly foliated structure. That the percentage diminishes as 

 the radius vector increases would in all probability be true ; its 

 becoming negative, however, may be due to some other causes. 

 The two series of experiments have been made under very different 

 surrounding conditions. The effect of moisture, for instance, is 

 never negligible as some observations were made during the wet 

 summer season ; while the others, during the dry cold of winter. 



Any complete discussion of the relation between the static 

 and the kinetic values must be postponed, at least, until the 

 effects of temperature and moisture on the elastic constants have 

 been clearlv investi 2;ated. The numerical values hitherto given 

 for the moduli of elasticity of several rocks must be taken only 

 as rouo'li estimates. 



