MAGNETIC DISTURBANCE 1389 
3. From the present investigation it seems that the anomalous 
vertical effect disappears at a radial distance of approximately 200 feet 
from the casing head, and it is the writer’s opinion that, for any com- 
mercial-size casing, this disturbance may be ignored at a distance of 500 
feet. 
4. In producing fields there appears to be no areal deformation of 
the vertical element, aside from the influence within the concentric zones 
surrounding the casing heads. 
107 
