434 
REPORT—1854. 
;trono« lfr 
change 
to M>®* 
On the Deviations of the Compass in Wooden and Iron Ships. 
By Archibald Smith, M.A. 
■ The general character of the deviations of the compasses of 1 ^ 
northern latitudes is, that the north end of the. needle is drawn ! ^ 
ships head. But in many, and particularly in iron shipj ,, the ch 
the deviations is different; in some the north end o . change« 
towards the stern, in others towards one side. I hese da ■*» * , ly 
the ship changes her magnetic latitude. In wooden P ) J „ e t],eir 
diminish as the ship approaches the magnetic equato , . j„ 
direction when the ship lias passed into a sou theim magnetic 1^.^ 
iron ships the deviations generally dimmish as the sh p. l P f0ut |,crn 
netic equator, but frequently, perhaps generally* increase b 
latitudes, so as to retain the same direction to both J ,e ' P the iron 
The cause of this difference, no doubt, is that in , j n the Ian- 
which affects the compass approximates to the conui 10 ’ r0 ]|ed and 
guage of magnetism, is called ,l soft iron," while in ,r ®“ * near |y to th« 
hammered iron of which they are constructed approach 
condition which is called “ hard iron.” annroaches vcfj 
In both classes of vessels a great part ot the mague i» ma gneii- nl 
nearly to that of “soft iron,” being induced instantaneous y In iron 
of the earth, and changing instantaneously as the vessc . g ° otf P tricilj 
vessels, the magnetism which approaches to that ot * lflr 11 ’ 
speaking, permanent; it is what is called "eub-pennanen y 
Royal, and “ retentive" by Dr. Scoresby. It is said by Dr* * ^ 
when the vessel receives strains or shocks, and it genera y 
extent when the vessel changes its magnetic latitude. ^ stained 
The general effect of masses of “ soft iron” on the nec J 0 f iron of A 
with considerable accuracy by considering the action V - n t j, e direc* 100 
very simple shape, viz. slender bars. A bar of soft, iron „ of t be «<>*"' 
of the dip, or, as it is convenient to call it, the “ hue o \ end attrac 
becomes instantly magnetic. Its south (in England, th . r 7 €n d) attr^ ' 
the north end of the needle; its north (in England, t e ( iiaiiiii^ lt5 ’ a0 i/ 
it. If the bar be inclined to the line of force, its magne magnetic* 
when at right angles to the line of force, the bar ceasesi nC reasw> 
the inclination of the bar to the line of force he still iu of the new • 
end which was north, and which then repelled the nortn 
becomes south and attracts it. , . „. r tical P oslti<M lL B . 
It follows from this, thut if a bar of 6oft iron be. m , fcU j 0 f < he ? • 
upper end will in north magnetic latitudes attract the n ea rtb a 
pass-needle. At the magnetic equator the line of * 0,rce nu tic. i j n 
zontal, and there a vertical bar of soft iron will not ^ j° u p\ranta 8,1 a 
magnetic latitudes the line of force of the earth is incline ^ r^j .then? 
those latitudes the upper end of a vertical bar of soft ,ro attraction 0 ^ 
end of the compass-needle, and attract the south end. nee dlc lD .. tb6 
upper end of such a bar of soft iron on the north endoi t , ie sin e ° a ^ e 
proportional to the total magnetic intensity multiple . nee dlebe ,Uc , ifi , 
magnetic inclination. The directive force of the earth on V, ucirl g a de«> 
antagonistic force which this attraction overcomes in P r( g 0 f the wf 
is proportional to the total intensity multiplied by l ” c . c0 \ tyr0 f° rceJ ’ 
tion. The deviation produced will be as the ratio of tnes 
