Dr. C. Davison on Earthquake-Sounds. 



65 



especially close to the ends of it ; and it followed it at 16 

 places chiefly near the epicentre or the shorter axis. 



Apparent Outracing of the Shock by the Sound. — The partial 

 coincidence of the sound with the shock at places near the 

 epicentre, and its precedence at others more distant, have led 

 some seismologists to believe that the sound-vibrations travel 

 with a greater velocity than those which constitute the per- 

 ceptible shock *. From the evidence of British earthquakes 

 we may conclude that the difference in velocity, if it exist, is 

 very slight ; for, otherwise, the sound could not be heard after 

 the shock at places so far distant as 180 miles from the 

 epicentre f. 



In the earthquakes of some other countries it would seem 

 that the sound generally ceases before the shock, and often 

 before the shock begins. In such cases there is clearly at least 

 an apparent outracing of the shock by the sound ; but it is 

 not improbable that this is due merely to the defective powers 

 of the observers for hearing the weak sound which follows the 

 shock. 



Relative Duration of the Sound and Sfioeh. — When the time- 

 relations of both beginning and end of the sound and shock 

 are noted by observers, it is generally possible to determine 

 their relative duration. The figures in the following table 

 give the number of records in which the duration of the 

 sound is greater than, equal to, or less than that of the 

 shock, as well as the number in which the relative duration is 

 doubtful. 



The most important figures in Table VIII. (p. 66) are those 

 which give the duration of the sound as greater or less than that 

 of the shock. Those which make the duration of both equal are 

 not entitled to the same consideration ; for the statement that 

 the sound and shock were coincident at both ends is less 

 precise than the others. We may therefore conclude that 

 the duration of the sound is generally greater than that of 

 the shock. 



* For instance, J. Druinmond, Phil. Mag. vol. xx. (1842) p. 240 ; 

 E. J. Lowe, Proc. British Meteor. Soc. vol. li. (1865) p. 55; H. J. 

 Johnston-Lavis, Geol. Mag. vol. ix.(1892) pp. 280-281; T. Tarauielli 

 and G. Mercalli, JR. Accad. dei Lincei, Memorie, fyc, vol. iii. (1885) p. 55, 

 and Annali deW TJff. Cent?: di Meteor, e Geod. vol. viii. (1888), parte iv. ; 

 M. Baratta, ibid. vol. iii. (1889) parte iii. 



f As at Baltinglass (co. Wicklow) in the Hereford earthquake of 

 1896. 



Phil. Mag. S. 5. Vol. 49. No. 296. Jan. 1900. 



