62 



Dr. C. Davison on Earthquake- Sounds. 



there being 276 earth-sounds and only 54 shocks and tremors. 

 If we divide the whole time into nine intervals of three 

 months each, the percentages of earth-sounds in the several 

 intervals are 87, 89, 88, 100, 95, 80, 50, 76, and 50 ; showing 

 that towards the close of the period considered, the perceptible 

 shocks increased in relative frequency. 



Time-Relations of the Sound and Shock. 



Jn earthquake-catalogues, the time-relations of the sound 

 and shock are not often recorded ; and it is therefore probable 

 that such entries, when they do occur, refer to the more 

 prominent relations. In Mallet's great catalogue, for instance, 

 the time- relations are given for only 423 earthquakes ; and 

 in these the sound is said to have preceded the shock in 100 

 cases, accompanied it in 307, followed it in 9, preceded and 

 accompanied it in 2, accompanied and followed it in 2, and 

 preceded, accompanied, and followed it in 3 cases. Thus, 

 either the sound occurred more frequently before the shock 

 than after, or the sound which preceded the shock was louder 

 and more readily observed than that which followed. 



In studying the more recent British earthquakes, I have 

 endeavoured to attain greater precision in defining the time- 

 relations of the three principal epochs of the sound and shock, 

 namely, the beginning, epoch of maximum intensity, and the 

 end. In the Table which follows, the letters ^>, c, and /indi- 

 cate the number of records in which any epoch of the sound 

 preceded, coincided with, and followed the corresponding 

 epoch of the shock. The first five shocks were all weak. 





Table VI. 















1 



! 



Earthquake. 



Beginning. 



Epoch of 

 Maximum 

 Intensity. 



End. 



1 



p. 



12 



1 



4 



5 



9 



59 



84 



80 



503 



c. 



3 

 4 



4 



ii 



35 

 16 

 71 



/. 

 1 



3 

 13 

 15 

 39 



1 

 p. c. 



/• 



i 

 p. 



c. 



/• 



i Cornwall, 1892 



1895 



1896 



1898 



... 1 



6 

 19 18 



:: : 



3 



5 

 9 



7 



1 



16 

 14 



7 

 72 



5 



2 



1 



4 



1 



6 



17 



11 



88 



8 



1 



2 



4 



16 



73 



55 



161 



51-7 

 56 9 



1 



Exmoor, 1894 



Leicester, 1893 



Pembroke, 1892 



1893 



19 



9 



25 



56 

 32 



85 



Hereford, 1896.. 



Percentage for each epoch, 

 weaker shocks 



721 



78 1 



25-6 

 143 



23 



7-5 



... 1000 

 _'5-l 66 6 



84 



3-5 

 20 3 



44-8 



22-8 



Ditto, stronger shocks . 



! 







