This paper is concerned with two different problems. The first of these is to correct a magnetic compass so that the essential relationships for zero deviation are maintained even when the ship rolls and pitches. The Harvey-Raynes corrector is described and its advantages are explained. This corrector makes it possible to steady the compass at any time without affecting the accuracy of the existing deviation card.

The second problem considered is the automatic correction of deviation for transmitting magnetic compasses. A system of ‘point-by-point’ correction is developed, based upon the representation of the deviating force by a truncated Fourier series; it is shown that such a truncated series may be represented mathematically in a form immediately suitable for practical application, some such forms being described in detail. It is shown that by means of a small additional device the ‘point-by-point’ type of corrector may be made to correct both variation and deviation, so that for any given part of the Earth the transmitting magnetic compass may be made to point true north.