SOME GEOPHYSICAL OBSERVATIONS AT BURRINJUCK. 453 



and Bega area, on 18th January, 1912, at 6*9 a.m. This 

 earthquake was felt over an area having a diameter of about 

 100 miles, and was recorded at the Riverview Observatory. 

 These earthquakes indicate that crustal equilibrium has 

 not yet been attained in this area. 

 The Records, 

 The records of each instrument from 22nd February 1915 

 to the 19th October of the same year are represented 

 graphically in the accompanying diagrams. The water 

 level is represented in each case by a curve, the ordinates of 

 which are proportional to the actual water levels recorded 

 at the dam. 



In the case of each pendulum boom the ordinates are 

 proportional to the actual displacements of the booms as 

 recorded on the photographic records. The actual deflec- 

 tions of the vertical for each instrument for the period 

 commencing 22nd February and ending 21st October 1915 

 are represented on the accompanying map (Plate LXII). 



In the case of the No. 1 Pendulum (the Heidelberg pen- 

 dulum established at Dale's tunnel), there was relatively 

 little movement of the booms while the water level was 

 slowly sinking, but both booms manifested considerable 

 activity when the water load was increased. The sense 

 of the movement is in the direction represented by an arrow 

 on the accompanying map. 



In the case of No. 2 Pendulum (the Strassburg Zollner- 

 suspension instrument, established at the Weighbridge 

 tunnel) the deflections of the vertical are also represented 

 on the map. The variations in the water level, however, 

 do not exert any marked corresponding influence on the 

 movements of the booms. This instrument is situated near 

 the dam, and is therefore subjected to the maximum stress 

 so far as depth of water is concerned ; and hence a small 

 rise or fall of the water level would represent only a 



