MAGNETIC DISTURBANCE 1379 
constant areal value of 7° 50’ east, along the magnetic north-south 
azimuth. 
Figure 4 shows the composition of the anomalous and normal com- 
ponents for a magnetic east-west traverse. The symmetry of the Z, R, 
H, and ¢ curves, as well as the relatively minor disturbance of the hori- 
zontal component and the dip, are apparent. The declination curve 
indicates a variation of 52° 30’ from a point 15 feet west of the casing to 
a corresponding position east. 
EXPERIMENTAL RESULTS 
To check the validity of the derived equations it was decided to take 
a series of actual observations along a magnetic north-south profile 
across the 206-foot string of casing represented by the foregoing theoret- 
ical curves. Vertical intensity measurements were chosen for the field 
investigations for the reason that, in the light of applied geomagnetics, 
this component assumes major importance. Further, it was felt that a 
comprehensive study of this single element would serve to test the au- 
thenticity of the various formulae in view of the mathematical relation 
between the several components. We therefore confine our comparison 
of the theoretical and experimental data to the vertical element. 
For these measurements a Schmidt vertical field balance was used, 
the magnetic system being maintained at a constant elevation of 102.4 
centimeters above a horizontal plane, through the upper end of the casing, 
to conform with the distance Og of Figure 1. The results for the north 
and south parts of the traverse agreed within the instrumental order of 
accuracy, mean values for the various positions being shown in Table I. 
TABLE I 
Distance DZ in 
in Feet Gammas 
fe) +32,402 
3-2 + 19,470 
6.6 ap OS 
12.0 + 1,988 
22.0 ae dig 
32.1 = ef) 
46.0 a 
56.0 — 6 
81.0 = =O 
118.5 = 29 
147.0 oa 14 
260.0 ° 
97 
