102 L. A. COTTON. 



innermost curve, therefore, represents the area of greatest 

 disturbance. An inspection of the isoseismals reveals a 

 systematic L shaped distribution of the curves, the signific- 

 ance of which is discussed below. 



As many of the reports furnished estimates of the direc- 

 tion of vibration, and as in most cases a sound was recorded 

 it was thought advisable to summarise this information 

 graphically in the form of a map. In Fig. 2 the boundary 

 of the sound area is represented. This conforms well with 

 the isoseismal curves and exhibits the same L shaped form. 



The directions of vibration are represented in direction 

 by straight lines, and in sense by the arrow head. The 

 points of the arrows are placed at the centres where the 

 observations were recorded. It will be seen from this map 

 that though the evidence is somewhat conflicting, yet on 

 the whole the directions of vibration correspond to the 

 distribution of the isoseismals. In view, however, of 

 Branner's investigations^ it is doubtful if the observed 

 directions of vibration have any real significance. 



Instrumental Evidence. 

 There are two seismograph stations within the area of 

 sensible shock. The first is that of the Riverview Obser- 

 vatory, and the second at the Sydney Observatory. 



The Rev. Father Pigot, S.J., has kindly allowed the 

 writer to examine the Riverview record, and Professor 

 Oooke has extended the same courtesy for the record of 

 the State Observatory at Sydney. 



The Riverview record was made by a Wiechert instru- 

 ment, while that of the Sydney observatory was made on a 

 Milne installation— photographically recorded. 



The total duration of the first and second preliminary 

 tremors could be accurately determined from the River- 

 view record, and amounted to 6*7 seconds. The record of 



