COMPAEISON OF EAETHQUAKE DIAGEAMS. 



65 



The horizontal and vertical motions thus measured may he 

 compounded together so as to make the complete tracing of the 

 motionpath of the earth -particles, which is then by referred to three 

 rectangular co-ordinate axes. By introducing the vertical component 

 to the already complex character of horizontal motion, we make the 

 result stUl more complex. Without going into details it will be ob- 

 served that at the seventh second while the ground was moving nearly 

 1 mm. in ES., it oscillated first 0.15 mm. downward and then 0.4 mm. 

 upward. In this and other parts of the principal disturbance the 

 period of vertical motion is less than one-half of that of horizontal 

 movement, or in other words for one to-and-fro oscillation of the soil 

 there are more than two simultaneous up-and-down strokes. 



The ratio of the maximum vertical to the maximum horizontal 

 motion is 1 to 5.3 for amplitude, and 1 to 3.3 for duration of dis- 

 turbance. 



PLATE X. AND PLATE XI. 



Eartliquahe of December 19th ^ 1885. — This was quite a severe 

 and extensive shock, sliaking the country within a radius of 160 miles 

 from its centre of disturbance, which was in the flattest part of Musashi 

 Plain, near the sea and 37 miles E. 35° N. from the Observatory. The 

 latter was in the midst of the affected portion of the country. No 

 damage was done by this shock. 



Instruments. — Plates X., and XL which are the records of the 

 above earthquake, are the exact repetition of Plates YIII. and IX. 

 respectively. The same instruments were used in both cases 

 under the same circumstances, except that the smaller plate was 

 turned in the opposite directions at the rate of 8-1 seconds to com- 

 plete one revolution, and the outer side of the East- West circle 

 was made to correspond to West and the inner side to East. 



