of the magnetic 'Needle. 191 
In the latter of these observations, the differences arising 
from a change in the direction of the ship’s head is less consi- 
derable than in the higher latitudes ; indeed, on approaching 
the line of no variation upon the south coast, the differences in 
the variation were smaller than before and afterwards ; but that 
these differences shall be greater in a large variation and smaller 
in a less, both places being equally distant from the magnetic 
pole, I will not venture to assert. The inferences that I think 
may be safely drawn from the above observations are as fol- 
lows : 1st. That there was a difference in the direction of the 
magnetic needle on board the Investigator when the ship’s 
head pointed to the east, and when it was directed westward. 
2d. That this difference was easterly when the ship’s head was 
west, and westerly when it was east. 3d. That when the ship's 
head was north or south the needle took the same direction or 
nearly so that it would on shore ; and shewed a variation from 
the true meridian, which was nearly the medium between what 
it showed when east and when west. 4th. That the error in 
variation was nearly proportionate to the number of points 
which the ship’s head was from the north or south. Constant 
employment upon practice has not allowed me to become much 
acquainted With theories, but the little information I have upon 
the subject of magnetism has led me to form some notion con- 
cerning the cause of these differences, and although most 
probably vague and unscientific, I trust for the candour of the 
learned in submitting it, as well as the inferences above drawn, 
to their judgment. 
1st. 1 suppose the attractive power of the different bodies in 
a ship, which are capable of affecting the compass, to be col- 
lected into something like a focal point or center of gravity, 
