IN THE IRON AND ARMOUR-PLATED SHIP NORTHUMBERLAND. 
493 
Table III. — Amount and direction of Magnetic Forces on 1st January 1867. 
\SS 
Ship’s force 
to head. 
X g 
Ship’s force 
to starboard. 
(ft — 1) tan 9 
Ship’s force 
downwards. 
X ViB 2 +® 2 
Horizontal 
force of ship. 
*»-■! 
Starboard 
angle of 
ship’s force. 
tan-i CoUIL 
V Col. IIP+IV 2 . 
Total force 
of ship. 
Col. IV. 
Dip of 
ship’s force. 
Standard 
-•562 
+ 062 
+ -553 
•566 
■791 
173f 
+44 24 
Starboard steering . . . 
-•546 
+ •186 
+ -139 
•578 
•595 
1614 
+13 32 
Poop 
-•691 
+•196 
+M63 
•720 
1-368 
164^ 
+52 46 
Port steering. 
-•580 
+ •242 
•628 
157+ 
Table IV. — 
Amount and direction of Magnetic Forces on 26th January 1867. 
Standard 
-•554 
+•094 
+•672 
•562 
•876 
170^: 
+50 5 
Starboard steering . . . 
-•037 
+•477 
+•620 
•478 
•783 
94,i 
+52 25 
Poop 
-051 
+ 175 
+ 035 
•181 
•184 
104| 
-10 57 
Port steering 
-•062 
-141 
•153 
246 
Table V. — Amount and direction of additional forces introduced between 
January 1st and 26th, 1867. 
Standard 
+•008 
+•032 
+ -119 
Starboard steering . . . 
+ ■509 
+•291 
+ -481 
•586 
•758 
+30 
+38 25 
Poop 
+ ■648 
-•021 
-M98 
•648 
1-362 
- 2 
-61 35 
Port steering 
+ ■518 
-•383 
•644 
— 36£ 
The values of B and C in Table I. show the remarkable amount of accordance in the 
deviations of the four compasses; a similarity which clearly indicates that the cause of 
the deviations is to be sought for, not in the iron in the immediate vicinity of those 
compasses, but in iron at such a distance that the distance between the compasses does 
not materially affect its action on them. 
The values of B and C in Table II. show an important change in three of the com- 
passes. The value of B for the starboard steering, poop, and port steering are nearly 
reduced to zero, showing the introduction of a powerful force attracting to the bow of 
the ship, or repelling from the stern. With C the case is very different; in the port 
compass a deviation to port is produced, in the starboard compassa deviation to star- 
board ; indicating the introduction of a repelling force between the two. The same 
conclusion may be drawn, and perhaps with greater facility, from a comparison of the 
value of the quantities in columns III. and IV. 
The quantities in columns V. and VI. show that the change produced is an upward 
force on the poop compass, and downward on the starboard steering compass ; pointing to 
a repelling force emanating from a point or region at a height intermediate between the 
height of the two compasses. These several comparisons show that the change was really 
caused by a repelling force (a north pole) being introduced in the iron of the poop- 
deck a little abaft the poop compass. 
The precise amount and direction of the force so introduced, and the changes it caused 
in the previously existing forces, will be seen distinctly by the mathematician from 
Tables III., IV., V. 
