52 
REPORT — 1854. 
vibratory or percussive action. He had also made experiments on a portion of a 
plate cut out of the side of a ship recently built, with effects exactly similar. The 
general results of his experiments went to the establishing of the fact, that, besides 
the two denominations of magnetism ordinarily received, that of simple terrestrial 
induction and that of permanent independent magnetism, there was another deno¬ 
mination corresponding with neither; not being absolutely controllable, like tl.e 
former, by terrestrial influences, nor capable, like the latter, of resisting all kind* 
and modes of mechanical violence. To this third denomination he hud given ita 
name of Retentive Mayve/imn. 
Dr. Scoresby then exhibited experiments with three sets of plates, two of iron and 
one of steel, for the illustrating of these several qualities of magnetism:—1. 'Hint of 
simple terrestrial induction by iron plntes free from polarity, which became lim¬ 
netic or changed their magnetism according to the position in which they were held. 
2 . Retentive magnetism, as illustrated by similar plates, which bad been previously 
magnetized by bending and blows, —such magnetism appearing as if permanent 
when the plates were moved about, without being vibrated or bent. And Srdlr. 
Permanent magnetism, as illustrated by an elastic steel plate, which, howewr 
violently it was bent or struck or vibrated, or in whatever position, still l’ r T, ir * c 1 
its magnetism unaltered. Now this retentive magnetism was the quality which b*' 
been prevalently considered us permanent; which, he was prepared to show, m 
by experiments on iron and facts of experience, was by no means a fixed q ua 1 
On the contrary, the long continued vibration of a ship under steam, and mud' 
so the straining of a ship in a heavy sea, under the circumstance when the tem: ■>« 
induction might be acting in a very different direction from the original axial po arr- 
ties of the Bhip, would be sufficient to change the direction of the magne'isni or 
gmally developed in the course of her construction. Hence much would d<T r ‘ • 
in respect of the mechanical action of the sea, on the position in which the Hip 
been built, or on the direction of her polar axis prior to such mechanical fon. 
In the case of the-Tayleur/ when he first hoard of the catastrophe, and bad * 
the evidence, he had stated to souie friends at Torquay, that lie would venture ^ 
pi edict that she hud boon built with her head easterly or north-easter y. . 
found, on inquiry, she had been built with lier head north-cast. Here, then. 
precise circumstances for expecting a change in the ship’s magnetic 
Having been built with her head to the north-east, she had a c t rt»i;< f| 
distribution accordingly, and when die began to strain, with her head * (0 
.t distribution was necessarily changed, and the first effect of it wa o ^ 
produce a great difference in the two compasses adjusted by fixed magnets- ^ 
captain had been aware of the changes which might, and roost probably woow. ^ 
place when the ship began to strain in a different position from that in « . ^ 
j®. J. een he had known that the compasses, having so large fU ;,> 
hLoil 00 as60 * rai 8 l ’tvary as much as two, or three, or even four points,''? 
v ■ n °wn, of course, that he must place no reliance upon them. , e9 Onf 
werp 'hb'i l 1 C< ? rn l ms6e5 wcre Of no use, because, under certain circum got 
32 i ab,C £ change. They should be, and were, of great use for aU 
Twp i h n WIShe ? to ,m l ,ri ' 88 «pon them was, that by attempting to * 
able influence by a permanent influence, they were liable to produce an«S8 
of erior. It was most important, therefore, for safety in navigating'‘ h hani;C n- 1 
, . • , , ' MiinuiiftiH, UIVlClUItTi IMI CttU M lkJ 
that captains should be made aware of the liability of the compasoes to*?^ 
so to mislead th«n; that they should know the circumstances undtr * { 
accordance with uutural laws regulating and applying the f art, ‘ 8tc bfoI ■' 
nnnZ’ "T WOit lik ely to «CCUr; that thev should be Jto 
JESTl f0 f ‘ )etcrn,ini, ‘t r the true magnetic direction with refer*a* 
a sTSrfr by ob * crv ? ,,on * of the sun and stars; and that by 
in 1820? ITT” ul ? ft (on the phm he. Dr. Scoresby, had suggested# 
miiht haw y. r ! Qm tbc deviating influence of the body of the ship “£-,*»** 
courlA «H», small altown^ces. *'«*&*»* 
anidied he n r c An< ! Wlb the precautions and means such ^, c t of < flP ‘ 
pEL Guidance InthlZ d, - d not doubt but tbat the difficx* 1 ; 1 ^ 
pass guidance, th avi « Bl,on of iron ships, might be mainly and prac 
