LINES OF MAGNETIC DECLINATION IN THE iiTLANTIC. 
183 
The aiTear was now found to be on the side of the hig-her dips, though probably to a 
much less amount than might have been the case had the observations been made at 
an earlier period after her return ; the tabular corrections which most nearly corre- 
spond to the observed disturbances are those of the dip —71° 28' instead of — 70° 40'. 
The expedition left Hobarton a second time in July 1841, passing the following 
(Antarctic) summer again in the regions of high southern dip, and returning to the 
Falkland Islands in April 1842, where the dip was between —52° and —53°; the 
observations on the disturbances of the eornpass were made in August, being about 
four months after the ship arrived ; an arrear however still remained on the side of 
the high dips in whieh several months had been passed previously to her arrival ; the 
tabular corrections corresponding to the disturbances are those belonging to a dip of 
between — 56° and —57°, instead of between —52° and —53°. 
From the Falkland Islands the Erebus sailed once more for the high latitudes in 
December 1842, returning, on this occasion, to the Cape of Good Hope in April 1843. 
She had now been in localities of higher southern dip than that of the Cape during 
nearly the whole of the three years whieh had elapsed since her former visit to the 
Cape, and she had passed the three months immediately antecedent to her second 
arrival, in dips varying from —60° to —65°, that of the Cape at the same period being 
— 53° 30'. The disturbances of the compass were examined on the 20th of April, 
being a very few days after her arrival at the Cape, and I find that the tabular cor- 
rections corresponding to them are those belonging to a dip of about —63° 30'. The 
arrear on this occasion was therefore about 10° on the side of the higher dips, it 
having been about 12° on the side of the lower dips when the ship arrived, in 1840, 
at the same station from localities of lower dip. 
The experiments at the Cape in April 1843 were the last, I understand, that were 
made in the Erebus during the progress of the voyage, for the purpose of examining 
the influence of the ship’s iron on her compass by tlie usual process of swinging the 
ship; and by an unfortunate misunderstanding, the repetition of the experiments on 
the return of the vessel to the Thames, which had been ordered by the Admiralty, 
and was fully designed to have taken place by Sir James Ross, was also omitted. 
It appears therefore that in every instance in which the proper experiments were 
made, the disturbances were found to be consistent with the hypothesis of an induced 
magnetism conforming gradually to the changes in the terrestrial magnetic pheno- 
mena occasioned by the changes in the ship’s geographical position, but not changing 
simultaneously with those changes. 
But whether the hypothesis of a gradual conformity of a part of the ship’s iron, 
instead of an instantaneous conformity of the whole, to changes of the terrestrial 
dip, be or be not the true explanation of the facts which have been thus pointed out, 
the facts themselves are highly deserving of consideration by those to whom the cor- 
rection of compass errors is of consequence ; the anomalies which present themselves 
to any previously entertained systematic view are of too large amount, as well as too 
consistent on the different points, both in the observations at sea and in harbour, to 
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