The PRECISION DEPTH RECORDER (fig. 17.5) is a fundamental 

 geophysical tool. The recording and measurement of depths 

 are controlling issues for nearly all of the other programs that 

 go on at sea. With this particular one it is possible to measure 

 to one fathom in 3,000. A narrow-beam vertically-pointing 

 sounder is needed in addition to the broad-beann sounders that 

 are prevalent today. Both are necessary, and each has its 

 own uses . 



Figure 17.6 illustrates a rather old MAGNETOMETER. New 

 ones are about a third or a quarter of this size. They are 

 used for nneasuring the total magnetic field. It would be 

 desirable to be able to include the measurement of declination 

 and variation, although this has not been done yet. Recently 

 our friends in Cambridge have demonstrated that the station- 

 ary type of nnagnetometer is very important in the oceans in 

 that the magnetic field variations with time at sea are not very 

 sinnilar to what they are on the nearby land. The corrections 

 we have been applying are not very reliable. 



182 



FIGURE I 7. 5 



PRECISION DEPTH RECORDER 



