372 



BE. CHAELES DAVISON ON THE 



[Aug. 1907, 



those of the second class, and by 95 per cent, of those of the third 

 class. The nature of the sound also differed in the three classes 

 of earthquakes, as shown in the following table (I), in which 

 the figures represent percentages for each class of earthquake to the 

 different types of sound. 













t>» 

































oS 





3 



Table I. 



a 5 

 •£ 









 .3 



=3 . 



02 



a 



.2 

 "02 





 © 



eB 





fcD c/j 

 ri £1, 



Si 





OS cjS 

 Hi 



1— 1 









Class i 



24 

 23 



16 

 9 



8 

 12 



10 



24 



29 



16 



12 



2 

 9 



Class ii 





- 



13 



3 



13 



30 



30 







Omitting the miscellaneous sounds in the last column, the first 

 three types may be regarded as of long, and the other as of short, 

 duration. In Class i 51 per cent, of the comparisons are of short 

 duration, in Class ii 52 per cent., and in Class iii 73 per cent. 



In the next table (II), the time-relations of the beginning and the 

 end of the sound and shock are given, the figures in the columns j9, c, 

 and / respectively representing the percentage for each class in 

 which the epoch of the sound preceded, coincided with, or followed, 

 the corresponding epoch of the shock. Under the heading ' relative 

 duration,' the figures in the columns headed g, e, and I represent 

 the percentages for each class in which the duration of the sound 

 was greater than, equal to, or less than that of the shock. 



Table II. 



Beginning. 



End. 



Relative 

 Duration. 



V 



c 



/ 



7 

 12 



P 



c 



/ 



9 



e 



I 



Class i 



49 

 36 

 36 



44 

 52 

 64 



15 



18 

 17 



55 

 57 

 83 



30 

 25 



44 

 35 



56 



65 



100 











Thus, the weaker the shock, the greater is the percentage of 

 audibility, the more numerous are the references to types of brief 

 duration, and the more closely does the sound approach to coincidence 

 with the shock. 



Length of Focus. — Taking the difference between the longer 

 and shorter axes of the inner isoseismal lines as a rough measure 



