216 DR. CHARLES DAVISON ON THE [May I904, 



Railway locomotive-department at Crewe. My debt to Mr. Arnold- 

 Bemrose may to some extent be realized by the statement that I 

 have to thank him for more than 170 records, many of them the 

 results of personal interviews with observers, for a classified series of 

 newspaper-reports, for the enlargement of the seismographic record 

 which appears in fig. 1 (p. 220), and for information on the geological 

 structure of the epicentral district. Without this timely aid, the 

 gaps in our knowledge of the Derby earthquake would have been 

 more serious, as well as more numerous, than those which at 

 present exist. 



The undoubted earthquakes were four in number, namely : 



a. March 24th, 1.30 p.m. (Principal earthquake.) 



b. March 24th, about 1.45 p.m. 



c. March 24th, about 5 p.m. 



d. May 3rd, 9.22 p.m. 



Besides these, eight other disturbances are reported, three before 

 and five after the principal earthquake, but the evidence is 

 insufficient to decide their seismic origin. They are as follows : — 



March 23rd, about 1.45 p.m. : Abbotshulme (near Rocester). Two persons 



felt a shock. 

 March 24th, about 5 a.m. : Kirk Langley. Two persons felt a shock similar 



to the principal shock. 

 March 24th, about 10.55 a.m. : Abbotshulme. One person felt a shock. 

 March 24th, about 1.50 p.m. : Tissington. A very slight shock. 

 March 25th, 0.30 a.m. : Fenny Bentley. A vibration without noise. 

 March 25th, about 6 a.m. : Draycott. A slight shock. 

 April 2nd, 2.30 a.m. : Duffield. A slight rumbling noise. 

 April 3rd, 1.17 a.m. : Duffield. A slight rumbling noise. 



The Principal Earthquake. 

 a. March 24th, 1.30 p.m. 



Intensity, 7 (nearly 8) ; centre of isoseismal 7, lat. 53° 3'1 ' N., long. 

 1° 41 '5' W. Number of records 1136, from 528 places; and 63 negative 

 records from 56 places. 



Time of Occurrence. 



The total number of records of the time is 565. Of these, 71 

 are considered by their observers to be accurate to the nearest 

 minute. Though two of them are as low as 1.25 and one as high 

 as 1.36 p.m., the majority lie between closer limits, 36 records 

 giving the time as 1.30, 10 as 1.31, and 8 as 1.32. The mean of 

 40 records from places within the isoseismal 6 is l h 30 m 15 s . 

 Three estimates are probably of greater value than the rest, namely, 

 l h 30 m 6 s for Derby (12 miles from the centre), l h 31 m for Alsager 

 (26 miles), and l h 31 m 5 s for Handforth, near Stockport (30 miles). 



In these three records no reference is made to the particular 

 epoch timed — an element of some importance, considering the long 

 duration of the movement. As will be seen in a later section, the 

 first tremors reached Birmingham (41 miles from the centre) at 

 l h 30 m 19 s , and Bids ton (Job miles) at l h 30 ra 44 s . Taking the 



