3H ELEMENTS OF ELECTRICITY AND MAGNETISM. 



4. Suppose that the semicircular error of the ship's compass 

 has been completely compensated and suppose that the quad- 

 rantal error is observed to be 4 to the west when the ship is headed 

 true northeast. What is the deviation of the compass when the 

 ship heads 30 south of east. Ans. 3 20' to the east. 



Note. In this problem treat the ship as one long slim iron bar parallel to the 

 keel. 



5. (a) A ship is headed true magnetic north (for which posi- 

 tion the quadrantal error is zero), and the compass shows a devia- 

 tion to the east. A permanent magnet is to be placed in an east- 

 west direction (athwartship) underneath the compass box so as 

 to bring the compass to true magnetic north. Which end of the 

 magnet is to be placed to the east ? (ft) The ship is then headed 

 true magnetic east and the compass is observed to have a devia- 

 tion to the west. A permanent magnet is to be placed in an east- 

 west direction (parallel to the keel) underneath the compass box 

 so as to bring the compass to true magnetic north. Which end 

 of the magnet is to be placed to the east ? Ans. (a) north end 

 east, (b) north end west. 



6. The semicircular and quadrantal errors having been com- 

 pensated the ship is headed magnetic south at sea and the com- 

 pass is deflected to the west when the ship heels to the east (top 

 of mast moves eastward). Which end of the heeling corrector 

 magnet must be placed upwards in order to eliminate the heeling 

 error? Ans. North end up. 



