ox THE EARTHQUAKE AND VOLCANIC THENOMENA OF JAPAN. 155 



For the latter investigation, the most desirable lists to use would be 

 those referring to shocks originating beneath the ocean or r.long tlie sea- 

 board, and as an assistance to this I give the preceding table, showing the 

 times of high water at full and new moon on the coasts for the fifteen 

 seismic districts shown in the small map. 



Nothing has been said about the possible i-elationship between earth- 

 quakes and volcanic eruptions, first, because we have no reason to believe 

 that, with the exception of a few feeble shocks which may precede or 

 accompany an eruption, there is any marked direct connection Ijetween 

 these two phenomena, and secondly, because the present catalogue does 

 not extend over a sufficiently long period of years to lend itself to such 

 an investigation. Although one or two new investigations have been 

 here suggested, the principal work will be a repetition of old analyses, 

 taking advantage of the fact that we are now able to deal with natural 

 districts, to give earthquakes, where required, relative weigh f/i, and to 

 distinguish between after shocks, the occurrence df which is but little 

 influenced by epigenic actions of long periodicity, and those of a district 

 where seismic strain is in a normal condition. 



As to whether seismology will be advanced by carrying out these and 

 other inquiries which may present themselves is a question which 

 cannot yet be answered. It may be or it may not be, but the catalogue, 

 which could not have been compiled without the generous assistance of 

 the Royal Society of London and the kindness of the director and 

 officers of the Imperial Meteorological Department of Japan, by allowing 

 access to their unequalled store of valuable facts, will, it is hoped, settle 

 the question as to whether it is desirable to continue in its present 

 form the largest and probably the most perfect seismic survey which has 

 hitherto been attempted. 



I am glad to say that some of the features presented by the catalogues 

 are now being analysed by Dr. C. G. Knott, of Edinburgh. 



(d) Fesulis alreachj obtained or shown hy the Catalogue and 

 Map of Centres. 



After Shocks. — About the time that the catalogue was commenced, 

 Mr. F. Omori undertook an examination of the shocks succeeding 

 the great earthquake of October 28, 1891. which are now indicated 

 upon the map in District No. 7. This he did, following up the in- 

 vestigation by an analysis of the disturbances since 1889 in District 11, 

 a series which recently occurred in District 10, and another series 

 belonging to a region lying between 8 and 9, which, although now 

 quiescent, about forty years ago was unusually active. As an outline of 

 Mr. Omori's investigations is published in the ' Seismological Journal,' 

 vol. iii. p. 71, and in greater detail in the 'Journal of the College of 

 Science,' vol. vii. Pai-t II., it would be out of place to give any detailed 

 reference to them here. Briefly, it seems that when a large disturbance 

 is followed by a long series of after shocks the number of these is roughly 

 proportional to the area first shaken, or what may provisionally be called 

 the intensity of the initial impulse. The character of the curves which 

 represent the freijuency of the after shocks in relation to time is 

 remarkably similar, and having determined by observation the form of 

 the eai'lier portions of a frequency curve, it seems possible to roughly 



