68 



HANDBOOK OF MAGNETIC COMPASS 



adjustment is made with the heeling magnet removed, it is now obvious 

 that other induction effects are introduced into the Flinders bar, in 

 addition to the induction from the earth's vertical field. These addi- 

 tional induction effects may increase or decrease the apparent correc- 

 tion effect of the Flinders bar, hence there is no simple correlation 

 between the length of Flinders bar and its visible deviation effect on 

 the compass. Likewise, any amount of permanent magnetism in the 

 Flinders bar will further distort the relation between the length of 

 bar and its visible deviation effect on the compass. These other induc- 

 tion effects cannot always be removed for such adjustments, as can the 

 heeling magnet, because the vertical permanent field is fixed with the 

 ship, and the removal of the fore-and-aft B magnets would destroy the 

 directive force on the compass. 



100. Heeling magnet induction in Flinders bar. — Figure 35 pre- 

 sents typical induction effects in the Flinders bar for different posi- 



Induction EFfects in 

 Flinders Bar 

 due to 

 Heeling Magnet 



Figure 35. 



tions of heeling magnet. An adjuster familiar with the nature of 

 these effects will appreciate the advantages of establishing the Flinders 

 bar and heeling magnet combination before leaving dockside. Devia- 

 tions must also be checked after adjusting the heeling magnet, if 

 Flinders bar is present. 



101. Corrector magnet inductions in spheres. — Should a ship 

 have spheres and many permanent B and C magnet correctors close 

 to the compass, there will be a condition of induction existing between 



