436 
REPORT —1854. 
pmSS'p.mV - U?: No ' vt Phil ' Tr ' ,844 ’ p - I17i and N '' VI "' 
=A+Vb' 
+ (c # 
tan 04- 
tan 0+ 
P' 
0 COS 0 
Q' 
0 cos 0 
^ sin £' 
j cos 4:' 
-I- D sin 2£'+E cos 2£', 
in which 5 represents the deviation, considered positive when the north end 
of the compass-needle is drawn towards the east; 0 the magnetic inclination; 
0 the total magnetic force; and £' the azimuth of the ship’s head by the 
standard compass (disturbed), reckoned from N. to E.; and A,B,C,D,E 
are constants depending on the arrangement of the soft iron in the ship, and 
the ship 011S<a,lt3 de P cnd '"£ paNly on the soft and partly on the hard iron in 
It we consider these terms separately, we see that A may (wise from such 
an arrangement of horizontal bars as that last described, or from an index- 
enoi in the compass, or from an error in the shore compass. 
1 15 1 9,n ^ “ positive, may arise from a vertical bar of soft in 1 ® 
p aced etore and below the compass, or abaft and above it. 
1 , u . cos ^ C' is positive, may arise from a vertical bar of soft ir» 
above it” ^ star ' i0a, ' t l side and below the compass, or on the port side a 1 
0 cos 0 Sin ^ ^ vos Jj cos £ must arise from iron having P ern,anfnl 
magnetism. 
placed ’ '* •?, ! a P os ‘t>ve, may arise from a horizontal bar of soft iro® 
is noifativ midship section, and cither before or abaft the compa® s -, 
the cnmlfi i may a !' iso from a horizontal liar of soft iron directed tow® 
£ . iUt at r 'gbt angles to the principal section. 1 .^ 
compass 2 h, lf ra - ay , ariS ^ fmm a horizontal bar of soft iron directed toward ^ 
being be’foJ IU ? ! nc<l 4 ' 5 ° to the bars in the last-mentioned case, ■ ^^ 
positive - anrlTV 0 lllC starl) °ard side, or abaft and to tbe P 01 ' s .' i ,idr ( 
Ff £ is i ; e8 n a f: v b c ef0re aud to tht rort side, or abaft and to the starboard - 
press ion for ‘ n tvhich B ' and P', C' and Q' are involved in 
in one geosrranP^i Cannot 1,0 separately determined from observa 10 
milled fvon ft P . 0sition - If ^ey "ere instants, they might ^ fC 
might then nro ,! e ['® l,ons made in any two geographical posi 1 1c |iang w 
its geoennfie ’i" * -*? c,,an K e which would take jilace when the ship 
« S But un fortunately the values of Ff* 
If we renm rc ‘ lia,1 ce can be placed on such determinations- 
6 represent th * value of the deviation by the simpler formula 
isA + Bsin V+C cos4 f +Dwii2£' + Ecos2£'# 
suggesf themselves° a,,d C ^present, then the following ^ 
th e A geM?r p 1 1 ical^2? epen r <,en * of th e dip and force, and 
latitude?; Ld thFs we “i 6 ,0 ? m ^ r vaS^ 3 
A and E being n d to be tIlc ewe, subject to this « b - e tho«g h 
U Uei " S Z CneraU y ' cry small, the changes in their value®. 
observ 
ratio 1 * 5 
