302 



Dr. C. Daviaon — BritisJi Eart]iqunJ;es. 



of 2h seconds, one part being so much ■weaker than the other that it 

 generally escaped notice. The first part was the stronger at Breaston, 

 Clifton, Edlaston, and Morley, and the second at Bradbourne and 

 Kirk Ireton. Of these places, Morley lies on the minor axis of the 

 isoseismals, Breaston, Clifton, and Edlaston on the south side of it, and 

 Bradbourne and Kirk Ireton on the north side. As the two parts 

 diifered considerably in strength, the observations on the relative 

 intensity of the two parts are more accurate than usual, and it may 

 therefore be concluded that a second focus lay a few miles north of the 

 Ashbourne focus, the concavity of the synkinetic band facing the second 

 focus. Thus the impulse in the Ashbourne focus was much the 

 stronger and occurred slightlj- before the other, but the interval 

 between the two impulses was less than the time required to traverse the 

 interfocal region. The earthquake was thus a true twin earthquake. 



Sheff^-tU 



Scixle <j/ l^TLlcs 



Fig. 3.— The Derby Earthquake, August 27th, 1906. 



The evidence is insufficient to determine the position of the second 

 focus. The mean interval between the two parts was, however, almost 

 exactly the same as in the earthquake of 1904 (2-6 seconds as compared 

 with 2'1 seconds), and it is therefore probable that the second focus 



