Part IV includes supplementary information which would be of interest to readers requiring additional information on electrical methods. The material includes both a physical and a theoretical description of how electrical current flows through the earth and how we can make sense of all the data we obtain in the field work. The final chapter provides a historical review of electrical measurements as applied to petroleum exploration, as well as some possibilities for future research.

The general approach in this volume is to bring together many ideas and observations which may be valid in electrical exploration, to clear up several misconceptions, and to present electrical data in a way which (hopefully) will help direct further effort in productive directions. However, the real advances of the science lie beyond the presentation of more electrical data. Only through dedicated research of anomaly mechanisms and through a sustained program of geophysical discoveries can the true potential of electrical techniques be fully realized as a valuable supplement to ongoing seismic and geologic exploration programs.