SOME GEOPHYSICAL OBSERVATIONS AT BURRINJUCK. 451 



photographic records 1 in the centre chamber. This three- 

 fold division also minimises the risk of air temperature 

 changes affecting the instruments during visits necessary 

 for changing the records. 



Both the pendulums and the recording apparatus are 

 mounted on solid concrete piers and are roofed over to 

 afford a protection against water seepage and small falls 

 of earth. 



The recording apparatus 2 for two of the instruments had 

 to be made in Sydney and the expenditure which this work 

 necessitated was met by a further grant from the Austral- 

 asian Association for the Advancement of Science. A full 

 account of the instruments and their installation will be 

 given in a later paper. 



The first of the instruments (the Heidelburg pendulum 

 established at Dale's Tunnel), was installed by Father Pigot 

 in May 1914, and all three instruments were recording in 

 October of that year. The records, however, have only 

 been yielding satisfactory results since February 1915. 

 Although the records obtained since that date are not 

 sufficiently extensive to be used as a basis for a quantitative 

 investigation, there are certain results of a qualitative 

 nature which are of extreme interest to both geologists 

 and geodesists. As it is proposed to continue the observa- 

 tions for a further period of two years before attempting a 

 quantitative statement, the writer was requested to make 

 such a preliminary statement as is now possible for the 

 information of those who are interested in this research. 



As a preliminary step towards the investigation it would 

 clearly have been desirable to ascertain as far as possible, 



1 Harrington's Limited are providing the photographic materials, and 

 are kindly giving special attention to ensure the greatest possible speed 

 for the paper. 



2 This recording apparatus was made by J. Cruikshank, Scientific 

 Instrument Maker, No. 9 Nicholson-street, Wooloomooloo. 



