Tilting deviations in magnetic declinations

Abstract

Experiments were made by swinging compasses in a wooden swing for the purpose of investigating deviations caused by the ship's rolling motion. Results obtained with various types of compasses are submitted in two tables. Dynamic deviations, the kinetic equilibrium error, and conditions other than those considered in these two theories are briefly discussed. Equations are given for computing the direction and relative strength of the apparent gravitational field as affected by the accelerations of the rolling motion. These are used to determine the maximum angle of tilt produced by the maximum angle of roll. The kinetic equilibrium error for an angle of tilt in one direction is shown to be different for an equal angle of tilt in the opposite direction for certain elements in certain directions of the axis of tilting and hence give rise to deviations. Examples are given for the three magnetic elements for instantaneous values of tilting. The computed deviation in declination that results in the case of a magnet having large moment of inertia, constrained to move about an axle parallel to the radius of swing, and having considerable damping has been found to be much smaller than would be indicated by the results of the experiments for the same conditions. It is concluded that this theory of tilting deviations does not account for the whole deviatipn observed and must be regarded as only contributing a part of the effect as does also the theory of dynamic deviations.