stations of about one-half mile, the resulting error in intlividual values 

 of A should amount to the equivalent of onh' a few tenths of a dynamic 

 millimeter in addition to such error as may be introduced through the 

 use of erroneous values of the vertical intensity of the earth's magnetic 

 field and of the proportionality factor. The values of (A-B) were 

 found to fluctuate widely, however, and reached numerical values of as 

 much as 17 dynamic centimeters and even greater values in the vicinity 

 of Loks Land and Davis Strait. The average value of (A-B) was 

 3 mm. ±68 mm. Excluding the six intervals from stations 3721 to 3724 

 in the approach to Loks Land and stations 3743 to 3746 in the vicinity 

 of Davis Strait where it is known that swift tidal currents exist, the 

 average value of (A-B) was still 3 mm. but with a variability of ±55 

 mm. Expressed as a gradient this average value amounts to only about 

 one-seventh mm. /mile. 



It will be seen from figure 38, however, that the value of (A-B) 

 changes irregularly from station to station and without dependence on 

 the length of the station interval. The upper section shown in figure 

 38, covering stations 3585 to 3576 shows the type of discrepancy dis- 

 tribution which had been expected, with small values of (A-B) in the 

 offshore part of the section and larger differences near the shoaler water 

 of the Grand Banks. Such sections as that from station 3627 to station 

 3617 where a discrepancy of 60 mm. occurs in the outer end of the 

 section and the inner end of the section has relatively small discrep- 

 ancies, have prevented the division of the area into two parts, one of 

 which is characterized by good agreement between the two methods. 

 The section including stations 3611 to 3616 illustrates an extreme dis- 

 crepancy of about 160 mm. Such sections as those including stations 

 3629 to 3638 and stations 3649 to 3639 show large discrepancies of about 

 60 mm. distributed throughout the section without regard to length of 

 station interval or location with respect to distance from the Grand 

 Banks. The section including stations 3716 to 3724 shows extreme 

 discrepancies of as much as 340 mm. in the approach to Loks Land 

 where swift tidal currents are known to exist, but it also shows a dis- 

 crepancy of nearly 100 mm. near the outer end which is located in the 

 middle of the Labrador Sea. 



No corrections were applied to the current meter results for geograph- 

 ical distribution of the vertical component of the earth's magnetic field 

 intensity and a constant value of 50,0007 was used throughout. While 

 chart values in the area of operation varied from 46,000 to 56,000 the 

 errors introduced by the use of the constant field intensity would affect 

 the absolute and average values of (A-B) but would not account for the 

 wide variation in (A-B) between adjacent pairs of stations. The pro- 

 portionality factor was taken as unity throughout the computations. 

 Although this factor changes considerably (between about 1 and 2) 

 from place to place in shallow water, von Arx reports that it is very nearly 

 constant at about 1.05 in water distant from land and deeper than 50 



95 



