54 
report— 1854. 
tion, changeable under severe straining and mechanical violence, 'which he has 
denominated retentive magnetism. 
Only one particular, that he is aware of, in Mr. Smith’s exposition, remains at all 
inaccordant with his (Dr. Scoresby’s) conclusions ; and that is the retaining, in the 
dase of two iron ships which have been swung at the Cape, of the deviation m its 
original direction. But this fact in so limited an experience cau prove little; ami 
even that to which it seems to point,—the existence of an apparent quality of per¬ 
manent magnetism, admits, he believes, of a simple (probable) explanation, namely, 
that the intense development of retentive magnetism in some heavy ranges o 
upright iron, such as the stern-post, &c., had not encountered sufficient mechauica 
violence to invert or obliterate their original polarity. , 
The circumstances under which the greatest magnetic and compass 
might be expected were then noticed. I . In new ships first encountering r y 
straining or rolling by the sea. Illustrated case, the 'Taylcur.’ 2. In snips g 
rally when first put on a voyage to a very different region. 3. In ships mngruu g 
on one course and then suddenly changing their direction. Cases of tne r • 
passing Cape Finisterre, other ships passing Cape Bon, and numerous ships ro 8 
the Cape of Good Hope —probably the ' Birkenhead.' 4. In ships procce mg ^ 
the southern hemisphere. Coses numerous. 5. Stroke of the sea. ' 8se 
' Ottawa.' 6. Stroke of lightning. Cose of the 'Bold Buccleugh. 
On the other hand, no large changes may be expected under these circu ^ 
— 1. In iron ships long in use, and ordinarily pursuing the same voyage 
temperate zone of the northern hemisphere; because the extreme or, g |na 5(ia ^ 
as occasioned by the oblique position of the ship’s magnetic polar axis, g 
down into a medium or normal position, out of which it is less liable to 
2. Hence in ships trading in our home channels or about our own coos ’ ecl< j 
ing the Atlantic in parallels not very much lower, the liability to new 0 
changes greatly diminishes. In such cases nn intelligent captain o • n 6 o(lUg 
changes of deviation in all his progress, outward and homewar » ^ 
the particular allowances and corrections, will generally be able to lun > 
course with considerable confidence. 
. U i uusci viug over me uuiwarns tor am puuiues, -- steering; or 
2. The avoidance of masses of iron in the immediate vicinity ot t (or else* 
other compass. 3. A reference compass aloft placed on the nnzcii i ret ] U cing 
where), clear of iron chains and iron work, as high ns may be requisi . ()|1 , 
the deviation to an unimportant quantity. This was the plan, an h t ], c extent 
(happily a practical and simple one) the author believes could ever re a w rt 
of the evil; a plan wluch he had himself adopted and recommence in 
placed before the public (Voyage of Researches and Discoveries in urt. _ 
the year 1823. 4. Care in selection of compasses to have e . j )V the 
Ihe author’s improvement*. unfortunately but slightly adopted, excep * 
Navy, had, since tlie year 1839 or 1840, trebled the ordinary power oi setlu | oUt ly 
needle, and rendered its endurance all but permanent. 5. Captains s . . the 
avail themselves of opportunities of testing their compasses, ana t ; on , !'• 
deviations on the courses steered, by azimuths and other modes of oes » ^ uf 
Captains should be specially informed nnd instructed on the ' liB bility w 
magnetism influencing the disturbing action of iron ships, ana i ion , , s i 
compass changes. For here, in addition to the ordinary dangers " * ta nt U> at 
peculiar source of error and misguidance, respecting which it is nioa 
the captain should never be thrown off his guard. m =tances ° n ^ cr 
In the course of his remarks. Dr. Scoreshy said that the circum d3 
which the 'Taylcur' had been built, as to the position of her “nttiug 1° Sl *’ 
N.h. and the vident straining and rolling she endured soon P o0 nt, a 5 .^ 
with her head ui a direction nearly opposite, or westerly, would fu ren iarka t l 
believed, on principles he had long maintained aud asserted, for tn 
change tn that unfortunate ship's compasses. 
