EARTHQUAKE MOTION TO GREAT DISTANt ES 



155 





the exact time of this commencement. The better market! group of waves on the 

 E. W. pendulum record seem to afford a more trustworthy time, and the other will 

 l>e discarded. 



Distinguishing the two shocks as (l)and (2) respectively, we get the following table 

 of time intervals in minutes : 



3. From the details given above it will be seen that of the eleven shocks, grouped 

 as seven earthquakes, which satisfied the conditions laid down, all gave threefold 

 records similar to that of the Indian earthquake of 1897. This, however, would not 

 of itself prove the correctness of the interpretation suggested in that case, nor even 

 that the three phases referred in each case to the same form of wave motion. To do 

 this it must be shown firstly that the intervals of time and space bear, in each case, 

 such relation to each other as will show that the three phases recognised refer to the 

 same forms of wave motion, and, secondly, that the forms of wave motion to which 

 they refer are those to which they have been assumed to be dxie. 



In carrying out this comparison it will be convenient to group and average the 

 observations in the case of each earthquake, not only in the case of each station, but 

 in each group of stations separated from the origin by approximately the same arc. 

 The limit taken will be 5, and the records from each group of stations lying within 

 this limit will be averaged. An exception will, however, be made in the case of the 

 instruments with photographic registration ; these, in spite, or perhaps because, of 



