6 DK. CHARLES DAVISON ON THE [Feb. I906, 



isoseismal 7 of the principal earthquake, and Norton about 8 miles 

 north of Doncaster. At about the same time, a rumbling noise was 

 heard at Bassingham (near Lincoln), and a shock was felt at North 

 Collingham (near Newark). In the absence of records from inter- 

 mediate places, it is uncertain whether the last favo observations 

 refer to a fore-shock connected with the Doncaster earthquake. 



III. Principal Earthquake. 

 (b) April 23rd, 1.37 a.m. 



Intensity, 7 ; centre of south-western portion of isoseismal 7, lat. 53° 26 - 3 r N., 

 long. 1° 1'2' W. ; centre of north-eastern portion of isoseismal 7, lat. 53° 36 - 5' N., 

 long. 0° 43-7' W. Number of records, 1428, from 662 places, and 68 negative 

 records from 66 places. 



Time of Occurrence. 



Excluding estimates that are given approximately, the total 

 number of records of the time is 695. Of these, 110 are regarded 

 by their observers as accurate to the nearest minute. The average 

 of the latter is 1.37 a.m., and, as the averages for the zones included 

 between successive isoseismals differ from this by less than half a 

 minute, it is probable that the time of occurrence at the epicentre 

 was almost exactly 1.37 a.m. 



Isoseismal Lines and Disturbed Area. 



The five continuous curves on the map of the earthquake (PI. II) 

 are isoseismal lines of intensities 7 to 3 ; the broken-and-dotted line 

 represents the boundary of the area disturbed by the earthquake of 

 April 13th, 1902. 



The isoseismal 7 consists of two portions, which are approximately 

 circular in form. The south-western and larger portion, which 

 is the most accurately drawn of the series, is 18| miles long from 

 north-east to south-west, 17| miles wide, and 244 square miles in 

 area. Its centre lies half a mile north of Bawtry, in lat. 53° 26*3' N., 

 long. 1° 1*2' W. The course of the north-eastern portion is some- 

 what uncertain towards the south-east, but probably does not vary 

 by more than a mile from the true position. As drawn, it is 

 9| miles long from north-east to south-west, 8J miles wide, and 

 63 square miles in area. Its centre is about 4 miles east of Crowle, 

 in lat. 53° 36*5' N., long. 0° 43-7' W., and lies 17 miles north-east 

 of the former. The centre of the disturbed area of the earthquake 

 of 1902 is in lat. 53° 33-4' N., long. 0° 41-5' W., or about 3 J miles 

 south-south-east of the centre of the north-eastern portion of the 

 isoseismal 7. 



The next isoseismal, corresponding to intensity 6, is roughly 

 elliptical in form, 58 miles in length, 44 miles in width, and 2050 

 square miles in area. The direction of its longer axis is E. 38° N. 

 and "W. 38° S. Its distances from the south-western portion of the 

 isoseismal 7 are 14 miles on the north-west side and 12^ miles on 



