CHAPTER XV. USE OF THE DIP NEEDLE FOR HEELING 



ADJUSTMENTS 



133. As indicated in chapter III, the heeling effects of both the 

 permanent and induced magnetism are corrected by adjusting the 

 position of the vertical permanent heeling Tnagnet. This adjust- 

 ment can be made in either of two ways : 



(1) With the ship on an even keel and as close to an east or 

 west magnetic heading as possible, adjust the heeling magnet 

 until a dip needle inserted in the compass position is balanced 

 at some predetermined position, 



(2) Adjust the heeling magnet while the ship is rolling on 

 north and south headings until the oscill&tions of the compass 

 card have been reduced to an average minimum. 



Inasmuch as it is desirable to establish the condition of induction 

 between the heeling magnet and Flinders bar and to reduce the heel- 

 ing oscillations to a minimum before making the adjustments at sea, 

 the heeling magnet is usually set at dockside by the first method 

 above. Further, it would be difficult to correct the heeling error by 

 rolling at sea before making the other adjustments because uncor- 

 rected horizontal errors would cause other oscillations of the com- 

 pass under rolling conditions. The spheres and Flinders bar produce 

 a certain measure of heeling correction and shielding effect, hence 

 they should be positioned (at least approximately) before making 

 the heeling adjustment by either method. 



Since the movement of soft iron correctors tends to change the 

 over-all heeling correction, and since the dip needle method of adjust- 

 ment is somewhat of an approximation method, such an adjustment 

 should be refined, if possible, by the rolling method after the other 

 phases of adjustment have been completed. This refinement should 

 be made just before taking the residual deviation curve. 



134. The fact that the heeling magnet corrects for induced effects 

 as well as permanent effects requires that it be readjusted with radical 

 magnetic latitude changes of the ship. Movement of the heeling 

 magnet, with Flinders bar in the holder, will change the induction 



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