﻿Vol. 6 i.l 



DEKBY EARTHQUAKES OP 1904. 



15 



equal to, or less than, that of the shock. The last line of the table 

 gives the percentages for the Derby earthquake of 1903 : — 



Table II. 



Beginning. 



End. 



Belative 

 Duration. 



P 



c 



30 



32. 

 24 

 24 



29 



37 



/ 







5 

 8 

 6 



6 



7 



P 



7 



24 

 12 



28 



18 

 21 



c 



47 



52 

 53 

 43 



51 



55 



/ 



47 



24 



35 



28 



31 

 24 



9 



71 



51 

 73 

 70 



62 



46 



e 



29 



39 



25 

 9 



31 



46 



I 







10 



2 

 22 



7 



9 



Within isoseismal 7 



70 



Between isoseismals 7 and 6 



62 



68 



6 ,, 5 



5 „ 4 



Whole sound-area 



„ ,, of the earthquake 



of 1903 



70 



• 



57 



For the epoch of maximum intensity, the number of records is 

 only 37. The epoch when the sound was loudest preceded that 

 when the shock was strongest in 30 per cent, of the records, 

 coincided with it in 62, and followed it in 8 per cent. 



The chief result of the foregoing table is the rough approach to 

 uniformity for the different zones, whatever their distance from 

 the epicentre. If the sound-waves travelled more rapidly than 

 those of larger amplitude, we should expect to find an increase 

 with distance in the observations of the sound before the shock, 

 and a decrease in those of the sound after the shock. Except in 

 the central area, in which both fore-sound and after-sound would 

 naturally be more sensible, there is no distinct trace of such 

 variation. 



IV. Aftek-Shock. 



c. July 3rd, 11.8 p.m. 



Intensity, 4; centre of isoseismal 4, in lat. 53° 2-8' N., long. 1° 39-5' W. 

 Number of* records, 76, from 42 places, and 2 negative records from 2 places 

 (map, p. 16). 



In the map of this after-shock (p. 16), the continuous lines repre- 

 sent the isoseismals 4 and 3, the dotted lines are the corresponding 

 isoseismals for the after-shock of May 3rd, 1903 ; the broken- 

 and-dotted line is the isoseismal 7 of the principal earthquake of 

 1904. 



The isoseismal 4 is 16 miles long, 10 miles wide, and contains 

 125 square miles. Its centre is about half-a-mile south-west of 

 Hognaston, and the direction of its longer axis about N. 27° E. 

 and S. 27° W. The course of the isoseismal 3 is somewhat doubtful 

 towards the north and south, but the error in either case is probably 

 less than a mile. As drawn, it is 27 miles long, 20 miles wide, 



