CHARACTER OR THE ARMOUR-PLATED SHIPS OF THE ROYAL NAVY. 281 
Standard Compass. 
33. 
e. 
Black Prince. 
November 1861 
. + -422 
+ •058 
September 1862 . . 
. -f-383 
+ •074 
July 1863 . . 
+ •384 
+ •067 
April 1864 . . 
, +-389 
+ •086 
October 1864 . . 
. +-349 
+ •050 
Resistance. 
August 1862 . , 
, +T49 
-•158 
June 1863 . . 
. +T52 
-•138 
December 1863 . . 
, +T06 
-•120 
December 1864 
. +-065 
-•153 
It will be remembered in the foregoing examples that the ships have been frequently 
subjected to the strains in docking, trials, in gales of wind, and at high rates of speed, 
and especially to concussions from the drilling and firing their heavy ordnance. 
A striking example of the permanency of the magnetism of an “ old ” iron ship after 
severe concussion is afibrded in the case of the Adventure troop-ship built in 1854. 
This ship, in the course of foreign service during a fog, struck on a rock with sufficient 
force to tear away and crush in 20 feet of the stem and bow under water ; appended 
are the coefficients observed before proceeding on the foreign service, and after the 
injuries sustained had been repaired in dock. 
1862. April 26th . . . = U73 + -186 
1862. October 28th , . — -07X + T86 
An equally close agreement will be fonnd, on reference to the Tables, to exist in the 
other magnetic coefficients of this ship ; the exact accordance of the numerical values is 
of course accidental, but is conclusive as to the great wear and tear and rough usage an 
old iron ship can undergo without her magnetic conditions being changed. 
4. The determination of the proportion of the semicircular deviation, or rather of B, 
which arises from vertical induction in soft iron, and that which arises from the perma- 
nent or subpermanent magnetism of hard iron, is a matter of great interest. Theore- 
tically it may be determined in two modes, either by observing the deviation in two 
different magnetic latitudes, or by observing the deviation with the ship upright and 
heeled over. Unfortunately there is a great want of observations under these circum- 
stances. The deviations of the iron-plated ships, given in the Tables, were carefully 
observed both at Lisbon and Gibraltar, but the difference of latitude between either 
place and England is too small, and the change in the subpermanent magnetism too 
great to enable us to derive any very certain results from these observations. 
The difficulty of heeling a large ship is so great that few observations except in an 
upright position can be expected ; we owe, however, to the zeal of the officers in com- 
mand of the Warrior*, Black Prince, and Defence, that these ships were swung at 
* Magnetip science is footed to the Honourable Captain Cochrane of Her Majesty’s Ship Warrior, for the 
interest he has evinced,, and the assistance he has rendered in obtaining poprplete records of that ship ; and 
2 q 2 
