APP. N** IX.] MAGNETICAL OBSERVATIOXS. 533 



From these observations, and from the assistance afforded 

 by the Kicid remarks of Captain FlinderSj the inferences 

 which follow are deduced *. 



1. In the construction of every ship, a large quantity of 

 iron being used, the portions thereof wliich liave a perpen- 

 dicular position, such as standard and hanging knees, the 

 nails and bolts in the deck, the capstevn spindle, flukes of 

 the anchors (when stowed as at sea), chain-plates, iron stan- 

 chions and riders; the eye-bolts, joint-bolts, transom-bolts, and 

 hind axle-tree bolts 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 tho 

 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. 



(a.) Tliat the attraction of a ship on the compass, depends 

 principally on such iron as has an upright position 

 there can be little doubt ; though I believe this ex- 

 planation of the cause of the anomaly in magnetic 

 observations made on ship-board, has not been before 

 suggested. This idea admits of a simple illustration. 

 Take any magnetic needle suspended on a centre, 

 a pocket compass, for Instance, and present to it 

 a bit of iron-wire, a nail, or any other piece of soft 

 iron of a lengthened form, not being magnetic, 



• The greater part of these inferences were drawn up during my voyage to 

 the whale-fishery in 1817; and the whole paper, as now given, excepting a few 

 notes that have been added, was sent to Sir Joseph Banks November 3, 1818, 

 and was read before the Royal Society on the 4th February 1819. The 

 additional notes are distinguished by the numbers prefixed being mclosed in 

 parentheses. A paper by Captain Sabine, " On irregularities observed in the 

 direction of the Compass needles of H. M. S. Isabella and Alexander, in their 

 late voyage of discovery, and caused by the attraction of the iron contained in 

 the ships," was also read before the Royal Society on February 18, 1819; and 

 another paper, by the same author, containing " Observations on the Dip and 

 Variation of the Magnetic needle, and on the Intensity of the Magnetic Force, 

 during the late Voyage in search of a North-west passage," was read on the 

 25th of the same montli. 3 



