Vol. 60.] DERBY EARTHQUAKES OF 1903. 217 



velocity afterwards calculated (p. 223) into account, it is clear that 

 the time of the first vibrations at the epicentre must be within a 

 very few seconds of l h 30 m s r.M., an estimate that agrees closely 

 with the mean recorded time within the isoseismal 6. 



Isoseismal Lines and Disturbed Area. 



On the map of the earthquake (PI. XIX) are shown five isoseismal 

 lines. The innermost, corresponding to an intensity of less than 8 

 according to the Rossi-Eorel scale, includes all the places but one 

 in which slight damage is known to have occurred to buildings. 

 In none was the injury more serious than the cracking of a poorly- 

 built wall, or the overthrow of a few chimney-pots accompanied 

 by the fall of some of the surrounding bricks. The bounding 

 curve is elliptical in form, 16^ miles long, 8| miles wide, and 112 

 square miles in area, the longer axis being directed X. 32^ c E. and 

 S. 32|° W. The centre of the curve coincides with the village of 

 Kniveton, which lies about 3 miles north-east of Ashbourne, in 

 lat. 53° 3-1' X., and long. 1° 41-5' W. 1 



The next isoseismal, of intensity 7, is 23| miles long, 17| miles 

 wide, and 272 square miles in area, with its longer axis running 

 X. 33° E. and S. 33° W. Its distance from the innermost isoseismal 

 is a little more than 3| miles on both sides of the axis. The 

 isoseismal 6 is 48 miles in length, 36 miles in width, and 1348 square 

 miles in area. Its longer axis is parallel to that of the isoseismal 7, 

 the distance between the curves being 12 miles on the north-west 

 side and 8 miles on the south-east. The isoseismal 5 is 76 miles 

 long, 69 miles wide, and contains 4060 square miles, its distance 

 from the isoseismal 6 being 17 miles towards the north-west and 

 16 miles towards the south-east. 



Still more nearly circular is the outermost isoseismal, that of 

 intensity 4, which, as drawn, is 129 miles long from north-west 

 to south-east, 126 miles from north-east to south-west, and 

 12,000 square miles in area : its distance from the isoseismal 5 

 being 35 miles on the north-west side, and 25 miles on the south- 

 east. Owing, however, to the difficulty always experienced in 

 obtaining observations from outlying regions, it is possible that the 

 path of this curve is inaccurately laid down, and that the diver- 

 gence of the curve towards the north-west is largely,if not entirely, 

 due to a defective series of records from other quarters. 



Records have also been received from a few places beyond this 

 isoseismal line — from Settle, Aysgarth, Richmond, and Easby 

 (1 mile east of Richmond), which are respectively 7^, 21, 27, and 

 27 miles north of the isoseismal, and from Boston, 12 miles farther 

 to the east. If the disturbed area were bounded by a circle 

 concentric with the isoseismal 4, it would contain 16,000 square 

 miles if the circle passed through Settle, 18,000 if through Boston, 



1 In a cottage at Alfreton (which is nearly 7 miles from the bounding curve) 

 a chimney-pot was thrown down, and some bricks in the chimney were 

 displaced. 



