462 



Prof. C. G. Knott. 



Table IV. The Coefficients c and a, the amplitudes and phase- 

 coefficients. 



A comparison of these times with the times of high water in the 

 various districts failed to establish any relation. We are forced to 

 the conclusion that if there be any lunar-diurnal periodicity imposed 

 upon earthquake frequency, it is the result of tidal stresses acting 

 directly on the approximately rigid crust of the earth, and not 

 indirectly through the loading due to the ocean tides. 



Because of the comparatively great number of earthquakes the 

 results for districts 6 and 7 a,re the most important. During the 

 eight years under discussion, the shocks in district 6 occurred with 

 normal frequency. All were comparatively small ; none were disas- 

 trous. On the other hand, the case of district 7 is altogether 

 peculiar. In general, this is a comparatively quiet district ; but the 

 great disaster of October 28, 1891, was followed by a vast number of 

 after-shocks. These show distinct daily and half-daily periodicities, 

 the latter having the greater amplitude. Thus, from district 6, with 

 its 1432 earthquakes distributed with fair uniformity over eight 

 years of normal activity, and from district 7 with its 3632 earth- 

 quakes, almost wholly included in a short fierce interval of fourteen 

 months, we obtain very similar evidence as to the existence of a 

 lunar half-daily period in earthquake frequency. 



The results for " All " depend, in the main, upon the statistics for 

 districts 6 and 7. The curious way in which the comparatively 

 prominent 1st harmonics of these two districts tend to cancel one 

 another, is a warning of the danger of lumping together statistics of 

 different countries or different seismic areas in the search for possible 

 periodicities. 



3. The Lunar Monthly and Fortnightly Periodicities. There are five 

 distinct kinds of months recognised by astronomers, namely : 



