150 R. i). Oldham — Tidal Periodicity in Earthquakes of Assam. [No. 3, 

 V. — Semidiurnal distribution of Shocks, 



Hours. 





 12 



1 

 13 



2 

 14 



3 



15 



4 

 16 



5 

 17 



6 

 18 



7 

 19 



8 

 20 



9 

 21 



10 

 22 



11 

 23 



All shocks h. to 11 h. 

 Do. 12 h. to 23 h. 

 Sum 



33 

 43 

 76 



44 

 43 

 87 



59 



48 



107 



55 



47 



102 



61 



71 



132 



57 



46 



103 



•97 



70 



48 



118 



111 



40 

 50 

 90 



•85 



41 



60 



101 



42 



71 



113 



43 



90 



133 



54 



58 



112 



105 



Sum 4- Mean 



•72 



•81 



101 



•96 



1-26 



•95 



106 



125 



Day shocks > 9° N. "^ 

 Night shocks > 9* S. 3 



80 



•82 



123 



•99 



M8 



•84 



Ml 



•67 



101 



•87 



152 



96. 



All shocks 9° X. to 9° S. 



•53 



•87 



•77 



120 1-61 



•84 



•94 



•97 



•94 



108 



114 



Ill 



• 



Day shocks >9<'N. ) 

 All shocks 9° N. 9° S. [ 

 Night shocks > 9° S. ; 



•69 



•84 



1-04 



r08 



r36 



•84 



104 



•80 



•98 



•95 



1*36 



102 



- ■ 



Night shocks > 9' N. \ 

 Day shocks > 9° S. j 



•77 



•77 



•94 



•71 



1^00 



f23 



1^26 



•94 



•94 



1*29 1*03 



112 



Here we see two very marked maxima, in the distribution of the 

 shocks, one during the fifth hour after, the other during the second 

 hour before, the meridian passage, and these maxima may be taken as 

 grouped around 4| hours and lOJ hours of the morning and afternoon. 

 That is to say they both follow by 1 J hours the epoch corresponding to 

 three hours before and after the meridian passage, a time which corres- 

 ponds more closely to the passage of the maximum rate of change of 

 tidal force, than to that of the circle of maximum horizontal stress. 



If we turn to the next line in the table, representing the distribu- 

 tion when the tide producing forces may be expected to be most effect- 

 ive we find the same features, except that the maximum following the 

 meridian passage is less marked than that which precedes it, and that 

 though the latter is proportionately greater than in the case of the 

 whole number of shocks the former is less. 



The next line shows the distribution when the sun is within 9° of 

 the Equator, when on the average the conditions — so far as the tide 

 generating forces are concerned — are the same during the day as the 

 night. Here we find the two maxima again, but it is that follow- 

 ing the meridian passage which is most conspicuous, the other being 

 small and ill defined. 



