4 DR. CHARLES DAVISON ON THE [Eeb. I9OCV 



fault-line cannot be ascertained from the seismic evidence : it must 

 lie on the north-western side of the centre of the isoseismal 4. A 

 line drawn through "Wendron in the direction mentioned above would 

 agree with all the phenomena known to me ; though one lying between 

 limits of \ mile to the south-east and 1 mile or so to the north-west 

 of this line would be equally suitable. 



Nature of the Shock. — Over a great part of the disturbed 

 area the nature of the shock was nearly uniform, and the following 

 account from Con stan tine may therefore be regarded as cha- 

 racteristic: — Two shocks, each lasting about 5 seconds, with an 

 interval of about 15 seconds between them, the second being the 

 stronger ; in both, the intensity gradually increased and then 

 died away, being greatest near the middle. The sound resembled 

 thunder, and overlapped the shock by about 3 seconds at both 

 ends : during the shock it appeared to be underneath the house, and 

 was then much louder and sharper. 



The most important feature is, no doubt, the double series of 

 vibrations. Two distinct shocks were recorded at 25 places : at 

 9 of these each shock was accompanied by sound ; at 12 others the 

 sound was heard, but, as in the account quoted above, the double 

 character is not recorded ; while in the remaining 4 no mention 

 is made of any sound being heard. Besides these, there were 6 

 other places where two distinct sounds were heard while no shock 

 was felt, and 1 where two sounds were heard without any reference 

 being made to the shock. 



With regard to the relative intensity of the two parts of the 

 shock, there can be little doubt that the second was everywhere the 

 stronger. At Mawnan, Mylor, and Tolvan Cross the second shock 

 was the stronger, and was accompanied by the louder noise ; the 

 second shock was the stronger at Constantine, Falmouth, Helston, 

 Penryn, and Ponsanooth ; and the second sound the louder at 

 Godolphin Cross, Mawnan Smith, and Porthleven. The only 

 exception to this statement occurs in the record from Binsey, 

 where the first sound is said to have been louder than the second ; 

 but as in other earthquakes there is always some variability in 

 the evidence on this point, it is not unlikely that this exception is 

 due to some misunderstanding. 



The estimates of the interval between the two parts of the shock, 

 as usual, differ rather widely, ranging from some seconds to 2 

 or 3 minutes, the average of 20 estimates being a little more 

 than 1 minute. Even supposing this to be much in excess of the 

 true value, it is evident that the first part must have been felt all 

 over its disturbed area before the occurrence of the second at the 

 focus. 



The boundary of the area within which the double shock was felt 

 is represented on the map (p. 2) by a broken line. It is 15 miles in 

 length, 10 miles in breadth, and includes an area of 116 square miles. 

 Its longer axis is directed E. 25° N". and W. 25° S., and is therefore 

 nearly parallel to the axes of the isoseismal lines. The centre of the 



