304 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



of every transverse slice, and therefore the field at C due to the 

 transverse magnetization of the entire ship when its bow points 

 east or west (magnetic) is towards the south, 

 T. and consequently the compass is not de- 



flected. 



b if 12. Compensation of quadrantal error. 



Quadrantal correctors. From Figs. 1 2 

 and 13 it is evident that the temporary 

 magnetism of the ship weakens the field at 

 the compass ( T opposite to H' in direction, 

 so that the resultant of T and H' is less 

 than H 1 ) when the ship heads north, east, 

 south or west. If the value of T is the 

 same in Figs. 12 and ij, it can be shown 

 that the temporary magnetism of the ship 

 does not tend to deflect the compass, what- 

 ever the direction of the bow of the vessel. 



To prove this proposition, we will assume 

 that the iron of the ship is equivalent to 



two long slim horizontal bars of iron, one parallel to the ship's 

 keel (the A-bar) and the other at right angles thereto (the B-bar). 



rB-bar 



60 IP 



Fig. 15. 



When the ship is headed north as shown in Fig. 14, the full value 

 of H 1 acts to magnetize the A-bar, and the magnetic field T v 



