64 s. SËKIYA. 



waves of the both components, i. e., waves in one chxle are some- 

 times in advance of those in the other circle or vice versa. This 

 means that the particles of the earth moved more or less in a cur- 

 vilinear path. At the twenty-third second there is a large East-A¥est 

 movement which has nothing to correspond with the North- South 

 components. On the contrary, from the thirty-third second a series of 

 vigorous undulations appear on the North- South components, while 

 that of the East- West is still at rest ; however at the thirty-sixth 

 second, the latter suddenly takes up its motion along with the former. 

 The measurements made at this point give a motion of 2.1 mm. in the 

 direction of N. 47° E. and S. 47° W. with a complete period of 0.8 

 seconds, which is the maximum horizontal motion registered in this 

 shock. 



On these points readers are reminded to compare Plates VIII. 

 and IX. and they will not fail to discover a close agreement between 

 them. 



During the interval of 80 seconds 91 complete waves may be 

 counted, which makes the average period of one complete wave equal 

 to 0.9 seconds. The undulations may be traced over one complete 

 revolution of Plate IX. making the duration 2 minutes 24 seconds. 



Vertical Motion. — The vertical motion begins at 0, but up to the 

 end of the sixth second it is nothing more than a series of very minute 

 tremours recurring from four to six times in a second. At the sixth 

 second when there is a large horizontal displacement, a vertical motion 

 of only 0.2 mm. is registered; at the seventh second it is 0.4 mm. with 

 a complete period of nearly 0.5 seconds, and is the maximum vertical 

 displacement in this shock; then the motion continues with com- 

 paratively large amplitude till the end of the fourteenth second. The 

 vertical motion may be traced up to the forty-fourth second, but the 

 subsequent disturbance is entirely in the horizontal plane. 



