Page:Popular Science Monthly Volume 34.djvu/319

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305
THE GUIDING-NEEDLE ON AN IRON SHIP.

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

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.