﻿DR. CHAKLES DAVISON ON TH3 [Feb. 1905. 



2. The Derby Earthquakes of July 3ed, 1904. By Charles 

 Dayison, ScJD., F.G.S. (Kead December 21st, 1904.) 



[Plate II— Map.] 

 I. Introduction. 



Between the Derby earthquakes of March 24th, 1903, and July 3rd, 

 1904, there exist several points of intimate resemblance. The 

 isoseismal lines of the two shocks, when drawn on one map, are 

 so closely related that they might be the isoseismals of a single 

 earthquake ; both earthquakes were twins ; the two epicentres in 

 1904 were nearly or quite coincident with those in 1903 ; and both 

 earthquakes were followed by an after-shock, originating for the 

 most part in the interfocal region of the fault. The points in which 

 they differ are of little consequence. The intensity of the shock of 

 1903 was greater than that of the shock of 1904 ; the impulses at 

 the two foci were approximately of the same strength in 1903, and 

 of unequal strength in 1904; they occurred at the same instant on 

 the former occasion, while, on the latter, they were separated by a 

 brief interval of time. 



The principal shock of 1903 occurred on a weekday at 1.30 p.m., 

 that of 1904 at 3.21 on a Sunday afternoon. Thus, although of less 

 intensity, the recent earthquake was felt and heard over a much 

 wider area than its predecessor. There was at the time practically 

 no traffic in the streets, and many of the observers (especially of 

 those at a great distance from the centre) were lying down — 

 conditions that favoured the observation of the earthquake in places 

 at which, on an ordinary occasion, it would have passed totally 

 unperceived. 1 



There were at least three earthquakes in the series of 1904, 

 namely : — 



(a) July 3rd, 2.28 p.m. 



(b) July 3rd, 3.21 p.m. (Principal earthquake.) 



(c) July 3rd, 11.8 p.m. 



In addition to these, disturbances resting on the authority of a 

 single record were reported at the following times : — 



July 3rd, 3.15 p.m. : Tissington. — Two persons, in one room, thought that 

 they heard thunder. 



1 I have to offer my best thanks to the very numerous observers who have 

 placed their accounts at my disposal ; to the editors of many newspapers who 

 have given a wide circulation to my requests for information ; and not least to 

 those who on this, as well as on the former, occasion have been so kind as to 

 collect records from other observers. Mr. H. H. Arnold-Bern rose has again 

 aided me materially in this way, as have also Sir John Gr. N. Alleyne, Bart. ; 

 Mr. W. Wells Bladen, honorary secretary of the North Staffordshire Field- 

 Club ; Mr. W. F. Blay, of Wallsall ; Mr. J. E. Bolton, of Eckington ; Mr. W. 

 J. Butcher, headmaster of the Grammar-School, Ashbourne ; Mr. J. Clark, of 



