MAGNETIC DISTURBANCE 1375 
Also, the resultant may be found from (5) and (6), thus 
4 
kas sa— | az + cany| 
m 
“ Pe LA Ge) SAE Ae cs aw 
4 
2 (ab + x2) (a2 + x)! (b2 + »| (7) 
The foregoing equations give values for the vertical, horizontal, and 
resultant forces of the anomalous field in gauss when the distances are 
expressed in centimeters and the pole strengths in c. g. s. units. 
The angle between the resultant dR and the OX— axis is termed 
the inclination, or dip, and may be found as follows: 
dZ ib (a? + x2)? — a (0? + 22)3 
ON re Cee ae 
(8) 
In Figure 2 are shown curves representing equations (5) to (8) in- 
clusive. These data were prepared from an investigation of a 206-foot 
vertical string of 10-inch casing, hating its upper end level with the 
earth surface. The pole strength of the casing was determined experi- 
mentally by measuring the vertical intensity anomaly directly above 
the pipe and solving for m in equation (5), it being assumed that / = 
0.833 L, and that the media surrounding the casing were of unit permea- 
bility. At a point 102.4 centimeters above the upper end of the pipe 
the anomaly was found to be 32,402 gammas." 
An examination of these curves reveals certain interesting charac- 
teristics. It is seen that the dZ and dR curves reach their maximum 
positive values directly over the casing, at which point they are numer- 
ically equal, because for this position the dH component is zero. At a 
radial distance of approximately 100 feet from the axis of the casing, dZ 
becomes zero and at 157 feet attains its maximum negative value of 
—102 gammas; at 260 feet the effect is reduced to —78 gammas. Ata 
distance of 17 feet from the casing the dH component reaches its max- 
imum amplitude of 12,500 gammas and at 75 feet appears equal to dR, 
because of the scale chosen. When the distance is increased to 260 feet 
the dH and dR values are 75 gammas and 108 gammas, respectively. 
"I gamma = 105 gauss. 
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