of the magnetic Needle. 189 
From some little change of place after tacking the ship, and 
from the part whose bearing was set not being perhaps the 
individual spot in both instances, the difference between the 
separate bearings in any set will not be always the same : to 
these causes for error also may be added inaccuracies in taking 
the angles arising from the motion of the ship and compass, 
from the view of the object being obstructed by the rigging, 
masts, or ship’s upper works, and from too much haste to get 
the bearings before the ship’s place was materially altered. 
Even in the Table of azimuths and amplitudes greater accuracy 
than one degree must not be looked for ; and in ship-bearings 
2 or even 3 degrees is not, I believe, too great an allowance 
for error, unless in very favourable circumstances. 
Without attending to small differences, it is evident that the 
bearings correspond with the observations in requiring a less 
east variation to be applied when the ship’s head was easterly, 
and a greater when it was to the westward, in order to get at 
the true direction of the object.* When examining the north 
• As a specimen of the plan I followed in protracting such bearings as the 3bove, 
take the set of April 15, AM, when the true variation appears to have been 4 0 E. On 
the first bearings the ship’s head was six points on one side of the meridian, and on 
the second it was three points on the other side, the mean is one point and an half 
on the east side ; now for this one point and an half I allow i° of error, which, as it is 
on the east side of the meridian, and the variation is easterly, must be subtracted : the 
variation then to be allowed upon the mean between the bearings before and after 
tacking will be 3 0 E, from which the true bearings will stand as follows : 
April 15th, AM |n western part - - - N I5°E 
n h 50' 3 A peaked hummock - - - N 20 E 
— Furthest extreme from deck - - - S 54 E 
— Centre of a naked sandy patch - - Eoj S. 
In the same manner upon single sets of bearings I was obliged to allow a variation 
different from what 1 supposed the true to be, unless the ship’s head was nearly north 
or south : but, that I might proceed as little upon conjecture as possible, I always 
