variation of the magnetic needle. 103 
last described, being ascertained by observation, the error 
on every other point of the compass may be easily calcu- 
lated; the anomalies produced by the attraction of the iron 
in the ship, being found to be proportionate to the sines of 
the angles between the ship's head and the magnetic me- 
ridian. 
Captain Flinders's rule is — As the sine of eight points (or 
radius) is to the sine of the angle between the ship's head and 
the magnetic meridian (or sine of the course reckoned from 
south or north) so is the anomaly found at east or west by 
observation, to the anomaly on the course steered ; or, 
the anomaly on any other course being found by obser- 
vation, the error on that position of the ship’s head “ would 
be to the error at east or west, at the same dip, as 
the sine of the angle between the ship's head and the mag- 
netic meridian, to the sine of eight points, or radius." 
8. A compass placed on either side of the ship's deck, di- 
rectly opposite to, or abreast of, the focus of attraction, gives 
a correct indication on an east or west course, but is subject to 
the greatest anomaly when the ship's head is north or south; 
and being here nearer the focus of attraction, the anomaly 
is much greater than that observed on an east or west course 
with the compass placed in the binnacle near the ship's 
stern. 
This inference is founded on observations, No. 1, 2,3, 8,9, 
13, 14, 1 5, and 17, of the prefixed table. The latter part 
of the inference, namely, that the greatest anomaly occurs 
here when the ship's head is north or south, is fully and 
uniformly established ; but the former part rests only on 
the authority of observations No. 8 and 9, though it derived 
