GEOMAGNETIC INVESTIGATIONS 



243 



The upper half of the double 

 sphere with the H-coil instrument 

 in position. Left, the amplifier; 

 centre, the accumulators which 

 supply the current to the motor 

 located below them; and right, 

 the recorder. 



Not unnaturally in a pioneer venture of this kind, and one involving 

 a continual race against time, various alterations had to be made in the 

 light of our experience as we went on. The spinning of the wire cable 

 caused our spheres to rotate at a speed which affected the accuracy of 

 the instruments. We solved this problem by means of a ball-and-socket 

 joint and a damping device, both specially constructed. After the preli- 

 minary surveys off Africa the instruments were returned to Copenhagen 

 and tested in a specially designed apparatus which reproduced the mo- 

 tions in the spheres. These were measured on the ship by means of a 

 special motion-measuring instrument sent out by air, the registered motions 

 being regularly radioed to the laboratory in Copenhagen. As a result of 

 this interesting cooperation in experimental physics between two groups 

 of workers at opposite ends of the Earth the instruments were re-designed, 

 and after a final check in Professor M. L. Oliphant's laboratory at the 

 University of Canberra were ready for operations in the Pacific. 



Meanwhile, the elasticity and watertightness of the spheres were tested 

 at extreme depths down to 10,060 metres off the Philippines. Unfortu- 

 nately, it is technically impossible to produce artificial pressure chambers 

 which can exert on objects 2.7 metres high an outward pressure of 1,000 

 atmospheres like that in these deep waters, and so we were obliged to 

 make the sea our laboratory. The double sphere came up fully watertight 



