In a grossly inaccurate discussion, Roy (1970) criticizes my analysis of screening factors for the electromagnetic response of a conducting sphere (Wait, 1969). The screening factor Sn was clearly defined in my paper as the ratio of two specified quantities.
The foregoing discussion by Dr. Thyssen-Bornemisza calls attention to interesting extensions of the rather simplified theoretical analysis in my paper. Dr. Thyssen-Bornemisza has published extensively on the subject of the vertical gradient of gravity and its applications in exploration. My paper was limited to a very specific topic, namely the variability of the vertical gradient along a vertical profile above an anomalous mass.