CORRECTION OF THE EFFECT OF HEELING. 187 



which is subject to induction, if so adjusted as to correct 

 W when the deck is level, will also correct Nin the heel- 

 ing term : and the part depending on cos 2A will dis- 

 appear. In ships where the steering compass is much 

 nearer the middle of the ship, N will usually be small. 



Supposing then that N is put out of consideration, 

 the term that remains is 



sin h x ( R tan dip + -=? j cos A. 



Both terms of the bracket become large in high mag- 

 netic latitudes, where the dip is large and H is small. 

 If K be positive, or tending to draw the red end down- 

 wards (as will hold in the subpermanent magnetism 

 produced by the operations in the process of building 

 iron ships in north latitudes), the second term, which is 

 the larger, will be negative ; and, remarking the sign of 

 cos A t when the ship's head is north of the east-and-west- 

 line, and the ship heels to starboard, the red end of the 

 needle will be drawn to the west : when the ship's 

 head is southerly of that line, the red end will be drawn 

 to the east. Both cases are included in the seaman,' s 

 rule " the red end of needle deviates to the windward 

 side." In southern magnetic latitudes, it is the blue 

 end which so deviates. 



When the ship's head is east or west, that is, when 

 A = 90 or 270, the heeling force vanishes: it is maxi- 

 mum, with different signs, when the ship's head is north 

 or south, that is, when A = or = 180. 



The circumstance that the deviating force is expressed 



