The welcome accorded to the first two editions of this book has been most encouraging. The object of the third edition continues to be to give a brief but "fairly comprehensive survey of the methods of applied geophysics including some of the modern interpretation techniques. The general approach and plan of the previous editions are preserved, but in bringing the book up to date some changes have been made to which I would like to draw the reader's special attention. SI units are strictly adhered to except in six illustrative figures reproduced from older literature and left intact to save some extensive redraughting. Following the recommendation of the International Union of Geodesy and Geophysics, the magnetic field measured in geophysical work is labelled here as flux density (tesla). Consequently, the symbols H, Z and T commonly used in geomagnetic work should stand for flux density. In the Max- wellian theory of electromagnetism the symbol H stands, by convention, for a magnetizing force (A m -1) and a discerning reader will at once sense a source of confusion. This source of confusion is avoided in the present edition by B , B and B instead of H, Z and T. The employing the symbols b z t latter ~et is employed for the corresponding magnetizing forces of the earth's field. I hope this notation will gain general acceptance because it so easily dispenses with an ambiguity that otherwise tends to lead to unnecessary confusion of units and dimensions in geomagnetism.

Table of Contents:
1 Introduction.- 2 Magnetic methods.- 2.1 Short history.- 2.2 The static magnetic field.- 2.3 Magnetic properties of rocks.- 2.4 The geomagnetic field.- 2.5 Instruments of magnetic surveying.- 2.6 Relative merits of ?Bh, ?BZ and ?Bt measurements.- 2.7 Field procedure.- 2.8 The interpretation of magnetic anomalies.- 2.9 Geological features.- 2.10 Anomalies of sheets and prisms.- 2.11 The Smith rules.- 2.12 Some examples of magnetic investigations.- 2.13 Measurement of susceptibility and remanence.- 3 Gravitational methods.- 3.1 Introduction.- 3.2 Gravimeters.- 3.3 Field procedure.- 3.4 Corrections to gravity observations.- 3.5 Marine gravity measurements.- 3.6 The Bouguer anomaly.- 3.7 Density determinations.- 3.8 Interpretation.- 3.9 Limitations on gravity interpretation.- 3.10 Depth determinations.- 3.11 Determination of total mass.- 3.12 Vertical derivatives of gravity.- 3.13 Illustrations of gravity surveys and interpretation.- 3.14 Note on the Eotvos torsion balance.- 3.15 Derivation of Formula (3.10c).- 4 Electrical methods.- 4.1 Introduction.- 4.2 Self-potential.- 4.3 Earth resistivity.- 4.4 Layered earth.- 4.5 Kernel function and resistivity transform.- 4.6 Determination of layered earth parameters.- 4.7 Vertical and dipping discontinuities.- 4.8 Electrical mapping, anisotropic earth and logging.- 4.9 The resistivity of rocks and minerals.- 5 Induced polarization.- 5.1 Introduction.- 5.2 Measures of IP.- 5.3 Origin of IP.- 5.4 Electromagnetic coupling.- 5.5 Example of an IP survey.- 6 Electromagnetic continuous wave, transient-field and telluric methods.- 6.1 Introduction.- 6.2 Near and far fields.- 6.3 Phase and polarization.- 6.4 Classification of continuous wave methods.- 6.5 The Compensator or Sundberg method.- 6.6 The Turam method.- 6.7 The moving source and receiver method (tandem outfits).- 6.8 Broadside and shoot-back techniques.- 6.9 Far-field methods.- 6.10 Theoretical approaches (continuous waves).- 6.11 Model experiments.- 6.12 Depth penetration.- 6.13 Transient-field methods (time-domain EM).- 6.14 Natural-field methods.- 6.15 Influence of magnetic permeability.- 6.16 Airborne measurements.- 6.17 Note on the design of electromagnetic coils.- 7 Seismic methods.- 7.1 Introduction.- 7.2 Elastic constants and waves.- 7.3 Instruments and field procedure.- 7.4 The refraction method.- 7.5 The reflection method.- 7.6 Corrections to arrival times.- 7.7 The seismic pulse.- 7.8 Filtering and geophone arrays.- 7.9 Convolution and synthetic seismograms.- 7.10 Deconvolution.- 7.11 Continuous velocity logging (CVL).- 7.12VIBROSEIS.- 8 Radioactivity methods.- 8.1 Introduction.- 8.2 Theoretical background.- 8.3 Radioactivity of rocks.- 8.4 Radiation detectors and field procedure.- 8.5 Radon measurements.- 8.6 Radioactive density determinations.- 8.7 Airborne radioactivity measurements.- 9 Miscellaneous methods and topics.- 9.1 Borehole magnetometer.- 9.2 Gamma-ray logging.- 9.3 Neutron logging.- 9.4 Geothermal methods.- 9.5 Geochemical prospecting.- 9.6 Optimum point and line spacing.- 9.7 Position location in airborne surveying.- 9.8 Composite surveys.- Appendix 1 Magnetic potential.- Appendix 2 Transition energy in the alkali vapour magnetometer.- Appendix 3 Magnetized sphere and a magnetic dipole.- Appendix 4 Magnetic potential of a linear dipole.- Appendix 5 Magnetic anomaly of a thick sheet.- Appendix 6 Potential of a point current electrode on the surface of a horizontally-layered earth.- Appendix 7 Fourier transforms and convolution.- References.