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variation of the magnetic needle. 
From these observations, and from the assistance afforded 
by the lucid remarks of Captain Flinders, the inferences 
which follow are deduced. 
1. In the construction of every ship, a large quantity of 
iron being used, the portions thereof which have a perpen- 
dicular position, such as standard and hanging knees, the nails 
and bolts in the deck, the capstern spindle, flukes of the 
anchors (when at sea), chain-plates, iron stanchions and riders; 
the eye bolts, transom bolts, joint bolts, &c. of gun carriages, 
and possibly the upper surfaces of the guns themselves, &c. &c. 
have a tendency to become magnetical, the upper ends being 
south poles and the lower north poles, in this hemisphere, 
where the north end of the needle dips, but the contrary in the 
southern hemisphere, where the south end of the needle dips. 
2. The combined influence of the iron distributed through 
all parts of the ship, seems to be concentred into a kind of 
magnetic focus of attraction, the principal south pole of which 
being upward in the northern hemisphere, is probably situ- 
ated, in general, near the middle of the upper deck, but 
nearer to the stem than the stern. 
Wrought iron having a much greater attraction for the 
magnetic needle than cast iron, the anchors, which usually 
lie about the bows, possess much more influence than guns; 
hence, the focus of attraction lies nearer to the bows than to 
the stern. 
3. This focus of attraction so influences the compass needle, 
that it is subject to an anomaly , or variation from the true 
meridian, different from what is observed by a compass on 
shore; the north point of the compass being constantly 
drawn towards the focus of attraction, which appears to be a 
