24 HANDBOOK OF MAGNETIC COMPASS 



(2) Fore-and-aft B permanent magnets in their trays, 



(3) Athwartship G permanent magnets in their trays, 



(4) Vertical soft iron Flinders bar in its external tube, 



(5) Soft iron spheres. 



Other type binnacles are shown in figures 39 to 43 inclusive. 



The heeling magnet is the only corrector which corrects for hoth 

 permanent and induced effects, and consequently must be readjusted 

 oGcasionalhf' %oith latitude changes of the ship. 



32. The tabular summary of "Compass Errors and Adjustments," 

 figure 19, summarizes all the various magnetic conditions in a ship, 

 the types of deviation curves they create, the correctors for each 

 effect, and headings on which each corrector is adjusted. Correctors 

 should be applied synmietrically under all but exceptional conditions 

 (discussed in detail later) and as far away from the compass as pos- 

 sible to preserve uniformity of magnetic fields about the compass 

 needle array. Other details of corrector procedure are emphasized 

 in chapter VIII. 



Fortunately, each magnetic effect has a slightly different charac- 

 teristic curve which makes identification and correction convenient. 

 A complete deviation curve can be analyzed for its different compo- 

 nents and thus the necessary corrections anticipated. A method for 

 analyzing such curves is described in chapter IV. 



33. Compass operation. — Figure 20 illustrates a point about com- 

 pass operation. Not only is an uncorrected compass subject to large 

 deviations, but there will be sectors in which the compass may slug- 

 gishly turn with the ship and other sectors in which the compass is 

 too unsteady to be used. These performances may be appreciated 

 by visualizing a ship with deviations as shown in figure 20, as it swings 

 from west through north toward east. Throughout this easterly swing 

 the compass deviation is growing more easterly ; and, whenever steer- 

 ing in this sector, the compass card sluggishly tries to follow the ship. 

 Similarly, there is an unsteady sector from east through south to west. 

 These sluggish and unsteady conditions are always characterized by 

 the positive and negative slopes in a deviation curve. These condi- 

 tions may also be associated with the maximum and minimum direc- 

 tive force acting on the compass. (See art. 19.) It will be observed 

 that the maximum deviation occurs at the point of average directive 

 force and that the zero deviations occur at the points of maximum and 

 minimum directive force. 



34. Correction of compass errors is generally achieved by applying 

 correctors so as to reduce the deviations of the compass for all headings 

 of the ship. Correction could be achieved, however, by applying cor- 

 rectors so as to equalize the directive forces across the compass posi- 



