310 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



The heeling corrector is a vertical steel magnet placed directly 

 beneath the compass box and adjusted up or down until it pro- 

 duces at the compass box a vertical field which is equal and oppo- 

 site to P '. The practical method of adjusting the heeling cor- 

 rector is explained in Art. 16. 



15. Compass errors due to magnetic lag. The temporary 

 magnetism of the ship's iron tends to lag behind the magnetic 

 field which produces it. Thus, after a ship has been standing for 

 some time in one direction the magnetism which is produced by 

 the earth's field does not at once disappear when the ship turns 

 around, but tends to persist. This magnetic lag produces a 

 compass error which is known as Gaussin's error and which cannot 

 be compensated. 



16. Directions for adjusting the correctors of a ship's compass. 



(a) Adjustment of semicircular correctors. The quadrantal error 

 is zero with ship's head north, east, south, or west. Therefore 

 any deviation of the compass which exists on these headings is 

 due to the semicircular error. With the ship's head north (mag- 

 netic), place one or more athwartship magnets in one of the semi- 

 circular-corrector trays and move them up or down until the 

 compass points north. Then head the ship east (magnetic) and 

 place fore and aft magnets in the other semicircular-corrector tray 

 and move them up or down until the compass points north. 



(b] Adjustment of quadrantal correctors. Having corrected 

 the semicircular deviation of the compass, head the vessel north- 

 east (magnetic) or southeast, southwest, or northwest, and if any 

 deviation of the compass exists, place the quadrantal spheres on 

 the side brackets of the binnacle and move them in or out until 

 the compass reading is correct. 



(c) Adjustment of the heeling corrector. With the ship headed 

 north or south in a heavy sea, place the heeling-corrector magnet 

 in its tube with its proper end upwards, and raise or lower it 

 until the slow motion of the compass due to the rolling motion 

 of the ship is nearly eliminated. The proper end up of the heeling- 



