AN INTRODUCTION TO THE SECOND DERIVATIVE CONTOUR METHOD OF INTERPRETING TORSION BALANCE DATA

After auspicious beginnings in the interpretation of torsion balance data, i.e., gradients and curvatures, the balance has been misused as a gravity instrument, the gradients being integrated into gravity, and the curvatures either neglected or not even observed in the field. Gravity was then made the sole basis of interpretation work, the regional effects being determined with more or less luck, subtracted from the total either before or after integration (regional gravity or regional gradient), and the residue held to be “local effect.” This method appears to be now in vogue for most torsion balance and gravity meter work. In contrast to this procedure, the method here described is based on the quantities measured directly by the torsion balance, the gradients and curvatures, or second derivatives, and constitutes a considerable amplification of the original methods of investigating these quantities. Gravity is simply a by‐product of this method, and is not needed at all for its functioning. The essential parts of this method are: 1) the re‐determination of all second derivative components with respect to a new system of rectangular coordinates, one axis of which has been made parallel to the direction of elongation of anomalous features; 2) the contouring of these second derivative components on four separate maps; and 3), the interpretation of the resulting contour patterns. The outstanding advantages of this method over the total gravity methods are the following: 1) full utilization of the two independent aspects of the gravitational field furnished by the gradients and curvatures; 2) virtual independence from regional effects; 3) much greater resolving power when compared to gravity; and 4), complete absence of assumptions, such as are involved in estimating the regional, and in computing gravity from the gradients.