22 ART. 10. — S. KUSAKABE. 



variables. It resembles a system of polar co-ordinates, but one 

 variable ' percentage ' is not proportional to an angle measured 

 from any fixed line. If a point p (f>i, n^ is given, then describe 

 a rightangled-isosceles triangle a2')h, with the given point as the 

 vertex and its base ab coinciding with AB. The two segments 

 Aa and Ab represent the corresponding values in the two dif- 

 ferent conditions referred to, provided one of the last segments is 

 taken as the unit of measurement. 



In Fig. 2, the modulus of elasticity is represented in this 

 co-ordinate system, its static and kinetic values corresponding to 

 a and ß respectively. It will be seen, at a glance, that when 

 the radius vector is relatively small almost every point lies on the 

 positive side, while a majority of those in which the radius vector 

 is somewhat greater lie on the negative side. Generally speaking, 

 so far as is shown by the present experiment, the percentage is 

 enormously large for a small radius vector, but diminishes as the 

 radius vector increases and ultimately it becomes even negative. 



That the percentage diminishes as the radius vector increases 

 is a matter of course, in so far as the phenomenon of yielding is 

 the principal cause which makes the two values differ from each 

 other. A negative value, however, can never be expected unless 

 some other cause or causes exist beside the phenomenon of 

 yielding. 



Examining more closely, we see that the percentage rapidly 

 diminishes and becomes even negative especially for those rocks 

 which have a foliated structure as in the case of schists and slates. 

 In schistose rocks, the percentage is generally negative as they 

 have large moduli of elasticity and, at the same time, a distinctly 

 foliated structure. Any eruptive rock, of whatever age it may be, 

 has a positive percentage. Of sedimentary rocks, those in which 



