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THE GUIDING-NEEDLE ON AN IRON SHIP.
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This force is resolvable into two others, the horizontal S H, and the vertical S Z; and the former is further divisible into S B, parallel to the midship line, and B H, transverse to it.
The magnetic power of the bar is thus resolved parallel to the
![](http://upload.wikimedia.org/wikipedia/commons/thumb/8/86/PSM_V34_D319_Magnetic_forces_of_a_ship_concentrated_on_three_planes.jpg/500px-PSM_V34_D319_Magnetic_forces_of_a_ship_concentrated_on_three_planes.jpg)
Fig. 15.—The Magnetic Forces of a Ship concentrated in Three Planes.
three co-ordinate axes. Almost all the structural iron of the ship—beams, knees, engines, boilers, etc.—is symmetrically arranged with reference to the vertical plane through the keel; so that for a piece T, on the starboard side, we should generally find another similarly disposed on the port side.