144 THE OCEAN RIVER 



the old-fashioned thermometer makes it one of the important 

 new weapons in the arsenal of ocean science. 



The most obvious and important thing about a current is 

 that it has a speed and a direction of its own, hence the meas- 

 urement of these is vital to such an expedition as Operation 

 Cabot. For over five centuries the computing of a ship's drift 

 has been the chief way to measure the pace of the Gulf 

 Stream, and Columbus' practice was improved on only 

 as more accurate methods of navigation were invented. Pills- 

 bury's current meter can be used only by a ship at anchor; 

 and the indirect calculation of currents from density measure- 

 ments is even more poorly adapted to rapid synoptic observa- 

 tion. But Operation Cabot was able to make use of a brand- 

 new instrument, the geomagnetic electrokinetograph — GEK 

 for short — which gives almost instantaneous information on 

 the direction and strength of water currents. 



This new instrument is based on an old principle that has 

 little apparent relation to oceanography. William von Arx, 

 who developed it, used the little-known fact that currents of 

 water in their passage through the salt ocean generate elec- 

 tricity, though in very small amounts. As the electric con- 

 ductors in a dynamo, passing between the poles of a magnet, 

 produce within themselves a flow of electricity, in the same 

 way sea water, itself an electrical conductor, develops an 

 electric current in its passage across the earth's magnetic field, 

 and the greater the speed of the stream the greater the elec- 

 tricity produced. Von Arx's instrument is simply a delicate 

 recording device that leaves an ink trace on a roll of paper 

 to tell the amount of electricity in water through which the 

 vessel in passing, and thus by simple calculation measures the 

 direction and strength of the water current. Thus the research 

 ship is no longer obliged to anchor or heave to when measur- 

 ing currents, but may do so when traveling at full speed — 

 and yet 2et a detailed answer . 



