Dr. a Davkon— British Earthquakes, 1893-'J9. Ill 



The isoseismal 4 is 11^ miles long, 4|^ miles broad, and includes 

 43 square miles ; the direction of its longer axis being W. 30° N. 

 and E. 30° S. Its centre is f mile W. 27° N. of Wells, and \ mile 

 from the corresponding centre for the first shock, the line joining 

 the two centres being parallel to the longer axis of both curves. 

 The distance between the isoseismals is nearly 3 miles on the north- 

 east side, and nearly 5 miles on the south-west side. 



In nature and duration the second shock resembled the first. It 

 was again a continuous series of vibrations, like that felt in a house 

 built directly over an underground railway, according to one 

 observer. The mean recorded duration was slightly less than 

 4 seconds, but most of the observers were awakened by the shock 

 and may have missed the earlier tremors. 



The sound is also compared to similar types. Among them may 

 be mentioned a goods train passing over an iron bridge, a deep 

 peal of thunder, a rushing wind, the fall of boxes on a floor, and 

 tremendously heavy blasting but prolonged. 



In estimating the frequency of comparison to different types, the 

 small number of descriptions renders it advisable to do so for the 

 two shocks together, especially as there are several other accounts 

 in which the particular shock is not distinguished. The sound is 

 compared to passing waggons, etc., in 26 per cent, of the i*ecords, 

 to thunder in 11 per cent., to wind in 5, loads of stones falling in 13, 

 heavy bodies falling in 11, explosions in 26, and to miscellaneous 

 sounds in 8 per cent. These are about the usual proportions for 

 a slight earthquake, except for the rather frequent references to 

 explosions. The exception is in reality only apparent, for, in all 

 but three cases, the reference is to an explosion prolonged or else 

 to an explosion in the midst of an undescribed rumbling sound ; the 

 three places are Wells, Wookey, and Wookey Hole, and these are 

 close to the epicentre. Again, the comparison to passing waggons 

 implies that the sound was of long duration and gradually increased 

 to a maximum and then died away ; but this is not the case with 

 the dragging of heavy boxes along the floor, which I have included 

 in the same type. Comparisons to the latter sound come from 

 Priddy, Street, and West Pennard, places which are not far from 

 the shorter axis of the disturbed areas. The general result is, as 

 we should infer, that the sound is of long duration near the ends 

 of the longer axis, and of short duration near the ends of the other. 



Belation between the two Earthquakes. — The relation between the 

 isoseismal lines of these two earthquakes is somewhat peculiar. 

 They are almost concentric. Yet both isoseismals of the second 

 shock overlap those of the first towards the east and west, and are 

 overlapped by them towards the north and south. Moreover, though 

 the second shock had the larger disturbed area yet its intensity was 

 not everywhere the greater. The first shock is reported to have 

 been the stronger at Binegar, Chewton Priory, Coxley, Dinder, 

 Priddy, Street, West Pennard, Wookey, and Wookey Hole ; and 

 the second shock at Croscombe, Draycot, Masbury, Pilton, Shepton 

 Mallet, and Wells. Now, at the points where the isoseismals 



