Yol. 65.] 



ANNIVERSARY ADDRESS OF THE PRESIDENT. 



lxxxvii 



with those obtained by Hecker, has arrived at a more exact 

 estimate of the amount of elastic yielding, and finds that it is much 

 less than would occur in a similar globe of steel. 



Thus, through the shifting sands of an ancient and prolonged 

 controversy, terra firma , indeed terra firmissima, has at length been 

 reached. 



Fig. 1. — Variation of the vertical under the influence of the moon. 



1 / / x \ 





\ 



_-< \ 



A \ 



— -0- \ \ 



// / v 



/// \ 



0/ t 



' / / / 



1 iff 



\ ill 



\ 

 \ 



\ 



\ 



15 u ""^ 



\ /'/ Pendulum 11./ 



sX \ / 



yy \ ' 



\ o/ 12 „ 



/ 

 / 

 / 

 / 



Pendulum I. / 



*r 



Continuous lines represent observed lunar curves ; the inner broken line 

 represents the observed semi-diurnal curve ; tbe outer broken line repre- 

 sents the theoretical lunar curve for an absolutely rigid earth.] 



A great future awaits seismic research. As Benndorf 1 happily 

 remarks, the sensitive instruments now employed to register the 

 movements of an earthquake are to the geologist what the spectro- 

 scope is to the astronomer : with the one we explore the depths of 



1 H. Benndorf, Mitth. Greol. Gesellsch. Wien, vol. i (1908) p. 336. 



