234 DR. CHARLES DAVISON ON THE [Aug. 1904, 



Til. Principal Earthquake. 

 b. June 19th, 10.4 a.m. 



Intensity. 7 : centre of isoseismal 7, lat. 53° 3'*0 N., long. 4 C 229' W. 

 Number of records. 388. from 206 places ; and 50 negative records from 44 

 places. 



Time of Occurrence. 



The total number of time-records (excluding those which are 

 confessedly approximate) is 176. Of these, 38 estimates are re- 

 garded by their observers as accurate to the nearest minute : the 

 average of 18 such estimates from places within the isoseismal 7 

 being 10 11 8 m 3 s a.m. As, however, the earthquake was registered 

 by seismographs at 10' 1 5 m 5 s at Bidston, and 10 h 5 m 56 s at 

 Birmingham, it would seem that the majority of railway-clocks, 

 and of others dependent on them, must have been kept about 

 4 minutes fast, and I have therefore deducted this amount from 

 the times given for all the shocks. 



Isoseismal Lines and Disturbed Area. 



The continuous lines in PI. XX, broken in parts where their course 

 is doubtful, represent the isoseismals 7 and 6, the boundary of the 

 disturbed area, and those portions of the isesoismals 5 and 4 which 

 traverse the land. In one or two places, buildings were slightly 

 damaged. At Clynnog, a slab of slate, weighing more than a 

 hundredweight, was dislodged from the top of a chimney ; and, at 

 Penygroes, two chimneys were thrown down. Both places are close 

 to the epicentre of the earthquake. 



The isoseismal 7 is an elongated ellipse, 334 miles long, 15 miles 

 wide, and 420 square miles in area. The centre is situated in 

 lat. 53° 3'-0 X., long. 4 22-9' AY., that is, 4 miles west of Penygroes 

 church, and the longer axis runs from X. 40° E. to S. 40° W. Of 

 the next isoseismal (6), little more than half can be drawn with any 

 approach to accuracy ; though the completed curve probably does 

 not deviate greatly from the path marked by the broken line. The 

 width of the curve is 38 miles, and its distance from the isoseismal 7 

 is 11*8 miles on the north-west side, and 10*6 miles on the south- 

 east. The isoseismal 5 is interrupted by the sea to the north of 

 Flintshire and in Caerdigan Bay. Its distance from the isoseismal 6 

 towards the south-east is 20 miles. Of the isoseismal 4, nearly half 

 can be drawn. It traverses the Isle of Man, and the eastern 

 counties of Ireland ; but its course in the latter district is doubtful. 

 Its distance from the isoseismal 5 towards the south-east is 27 

 miles. 



The outermost isoseismal drawn corresponds to an intensity 

 between 4 and 3. It is 185 miles in length from north-east to 

 south-west, 173 miles wide, and contains 25,000 square miles. The 

 shock was also felt at four nlaces outside this line — at Dun more 



