116 HANDBOOK OF MAGNETIC COMPASS 



effects in the Flinders bar and thus change the compass deviations. 

 (See article 100.) Thus, the navigator is responsible for : 



(1) Moving the heeling magnet up or down (invert when 

 necessary) as the ship changes magnetic latitude so as to main- 

 tain a good heeling adjustment for all latitudes. 



(2) Maintaining a check on his deviations and noting changes 

 resulting from movements of the heeling magnet when Flinders 

 bar is in the holder. Any deviation changes should be either 

 recorded or readjusted by means of the fore-and-aft B magnets. 



135. To elaborate on the details of the dip needle method of ad- 

 justment, it is pointed out that there are two types of dip needles: 

 one which assumes the angle of inclination, or dip, for its particular 

 location, and one on which the magnetic torque is balanced by a mov- 

 able weight. The latter is a nullifying type instrument which ren- 

 ders the final position of the needle more independent of the hori- 

 zontal component of magnetic fields, and hence is more useful on 

 uncorrected compasses. 



For ships which introduce no shielding to the, earth's field at the 

 compass, the procedure for adjusting the heeling magnet is quite 

 simple. Take the dip needle into a nearby area where there is no 

 local magnetic distraction, level the instrument, and set the weight 

 so as to balance the needle under those conditions of earth's magnetic 

 field. It is preferable to align the instrument such that the north 

 seeking end of the needle is pointing north. Next, level the instru- 

 ment in the compass position on board ship, place the spheres in their 

 approximate position, and adjust the heeling magnet until the needle 

 assumes the balanced condition. This presumes that all the effects 

 of the ship are canceled, leaving only the effect of the vertical earth's 

 field. The degaussing circuits are secured during this adjustment. 



In the case of ships which have shielding effects on the earth's field 

 at the compass, as in metal enclosed wheelhouses, the procedure is 

 essentially the same as above, except that the weight on the dip needle 

 should be moved toward the pivot so as to balance against some lesser 

 value of earth's field. The new position of the weight, expressed in 

 centimeters from the pivot, can be approximately determined by mul- 

 tiplying the value of lambda^ A, for the compass location by the original 

 distance of the weight from the pivot in centimeters. Should lambda, 

 A, for the compass location be unknown, it may generally be con- 

 sidered as about 0.8 for steering compass locations and 0.9 for stand- 

 ard compass locations. By either method, the weight on the dip needle 

 should be moved in to its new position. Next, level the instrument in 



