120 Capt. Sabine on irregularities observed 
might receive an absolute increase in the intensity of its 
attractive power by approaching the magnetic pole. 
The increase, however, which was the subject of his obser- 
vation, was a relative one, being in comparison to the directive 
power of magnetism. A diminution in the latter would 
therefore produce the effect equally with an absolute augmen- 
tation in the former; and that such a diminution does take 
place, and in a degree which is sufficient to account for all 
the effects observed, will be evident to every person, who 
reflects that although the magnetic force is greatest at the 
pole, its directive power must then have wholly ceased, 
having become less on the horizontal traversing of the needle 
in proportion as the point of attraction has been brought 
beneath the compass ; indicated by the angle which the 
dipping needle makes with the horizon. This is doubtless 
the principal cause of the connection which Captain Flinders 
was the first to trace. 
It is not designed to say that this cause may not be 
aided by the increased magnetism of portions of the ship's 
iron, such as bars and stanchions ; which being fixed in an 
upright position, may receive an addition to their attractive 
power where the position of the dipping needle is always co- 
incident with theirs; but merely to observe, that. a cause is 
known to exist for the connection, independently of supposi- 
tion ; which cause, conjointly with experience, shows the 
inadequacy of the rule proposed by Captain Flinders, whereby 
the amount of error, under any known dip, being ascertained, 
the amount may be calculated for any other dip, by using as 
a multiplier, the decimal expression of the proportion which 
