244 



GEOMAGNETIC INVESTIGATIONS 



The single sphere coming up the shaft on the way out. 



from all depths, including 7,000 metres, the lowest depth at which we 

 were able to test it, but the single sphere contained a couple of litres of 

 sea water. As this sphere had been cast first and the casting of a new 

 alloy is a difficult process, there was nothing remarkable in the incon- 

 sistancy, which was thought to be due to casting stresses. We made various 

 grindings of the single sphere on instructions sent out from the factory by 

 radio, and in due course succeeded in equalizing the stresses so far that 

 only a couple of cubic centimetres of water seeped in even at extreme 

 depths. The instruments could easily be protected against this. 



The final magnetic work was carried out in the Kermadec-Tonga 

 Trench and in the Gulf of Panama. After \'arious preliminary surveys to 

 test the adjusting and handling of the instruments at sea, the effect of the 

 ship's manoeuvres on the measuring, the influence of bottom conditions, 

 and so forth, measurements were eventually made, on May 10 — 11, 1952, 

 at a depth of between 3,000 and 4,000 metres and with the desired accuracy 

 of about 10 gammas. Unfortunately, owing to lack of time, they were 

 made at only one station and the measurements were disturbed by the 

 proximity of the bottom. Nevertheless, by demonstrating that it is techni- 



