Is addition of induction vectors meaningful?

Justification is given for using the word ‘vector’ (with its mathematical implications) to describe the arrows first employed by Parkinson and Wiese to depict induced magnetic variation fields associated with conductivity anomalies. Despite this, caution should be exercised when trying to interpret physically the resultant obtained by adding or subtracting such vectors. Induction in a rectangular surface anomaly near a coastline is investigated numerically with the aid of a thin sheet program for inducing fields of periods 1 h and 20 min. It is found that in certain regions the induction vectors for this configuration are not given by the resultants of the separate induction vectors for the coastline and anomaly alone unless the anomaly is so far removed from the coastline that there is little electromagnetic coupling between them.