Vol. 62. J DOS CASTER EARTHQUAKE OF 1905. 7 



the south-east side, and, from the north-eastern portion of the same 

 curve, 14 and 16 miles respective!} 7 . 



The remaining isoseismals are somewhat less accurately drawn, 

 and, in parts, may possibly vary as much as 2 or 3 miles from 

 their true position. The deviation cannot, however, be of much 

 consequence. The isoseismal 5 is 90 miles long from north-east 

 to south-west, 76 miles wide, and contains 5300 square miles; its 

 distance from the isoseismal 6 is 14 miles on the north-west, and 

 18 miles on the south-east side. The isoseismal 4 is 126 miles 

 long from north-east to south-west, 108 miles wide, and about 

 10,700 square miles in area, and is distant 16 miles in both 

 directions from the isoseismal 5. The isoseismal 3 is 166 miles 

 long from north-east to south-west, 130 miles wide, and about 

 17,000 square miles in area, its distance from the isoseismal 4 

 being 14 miles towards the north-west and 21 miles towards the 

 south-east. I have also received records from several places out- 

 side the isoseismal 3 — from Liverpool, Lingen (in Herefordshire), 

 Hugglecote and Winchcombe (in Gloucestershire), Soham (in Cam- 

 bridgeshire), and Norwich ; but I do not feel sure that the move- 

 ments observed at these places were connected with the Doncaster 

 earthquake. The area apparently disturbed by the earthquake was 

 therefore about 17,000 square miles. 



Nature of the Shock. 



The twin-character of the shock was clearly recognized throughout 

 a district overlapping the isoseismal 5 by a few miles in every 

 direction, and was sensible to some observers as far as, and in three 

 cases beyond, the isoseismal 4. Over the whole disturbed area, 

 32 per cent, (or roughly 1 in 3) of the observers who noticed 

 closely the nature of the shock detected either two maxima in a 

 continuous series of vibrations, or two detached series of vibrations 

 separated by an interval of a few seconds. The percentage varies 

 in different districts, being 31 within the isoseismal 7, 38 between 

 the isoseismals 7 and 6, 32 between the isoseismals 6 and 5, and 14 

 between the isoseismals 5 and 4. These variations and the com- 

 paratively-small percentage are due: (1) at places within the 

 isoseismal 5, and especially near the epicentres, to the perception of 

 a continuous tremor between the two parts of the shock ; and (2), 

 at places outside the isoseismal 5, to the enfeeblement of the vibra- 

 tions composing the weaker part. Thus, at Balne (9 miles north 

 of Doncaster), the movement was continuous and contained two 

 maxima, the first of which was the stronger; at Sheffield, the 

 intervening tremor was less sensible, and the shock consisted of two 

 detached parts separated by an interval of one second, the first 

 being slightly stronger than the second ; at Thornton Curtis (9 miles 

 north-east of Brigg), two series were felt, of which the second was the 

 stronger, the interval between them being 3 or 4 seconds, and also 

 two distinct sounds were heard, of which the second was the louder 

 and separated from the first by 2 or 3 seconds ; and, lastly, at 



