144 L. A. COTTON. 



One of the three pendulums is that which was employed 

 by Hecker at Potsdam in his classical investigation on 

 earth tides, and another was used by Schweydar at Heidel- 

 berg for the same purpose. These are both of the Rebeur- 

 Bhlert type. The third instrument is of the Zollner 

 suspension type and was specially constructed to Hecker's 

 design* The installation and maintenance of the pendulums 

 atBurrinjuck havebeen provided forunderthe joint auspices 

 of the State Irrigation Commission and the Australasian 

 Association for the Advancement of Science. 



The pendulums are housed in tunnels the sites of which 

 were jointly chosen by Professor David, Father Pigot, Mr. 

 D. F. Campbell, and the author. These tunnels are placed 

 from 20 to 40 feet above the highest water level, and are 

 from 60 to 80 feet in length. 



The design of the installation was prepared by Father 

 Pigot, who also set up the first of the pendulums in May 

 1914. The instruments were finally adjusted by the writer 

 and all three were in working order in October of the same 

 year. Their care has since been in his charge. 



A preliminary account of the deflections of the earth's 

 crust during the first year of the records has been already 

 published 1 and it is only necessary to review briefly this 

 work. It was pointed out in this preliminary account that 

 four types of earth movements have been recognised. 

 These are as follows : — 



(1) Earth tides. (3) Fault movements. 



(2) Earthquakes. (4) Slow deflections of the vertical. 



These movements are briefly discussed in the paper above 

 mentioned. This communication is only concerned with 

 the movements of the fourtn type. The study of these 

 indicates that many of them occur synchronously with 



1 Leo A. Cotton, " Some Geo-physical Observations at Burrinjuck/ 

 This Journal, xlix, 1915, pp. 448-462. 



