THE GUIDING-NEEDLE ON AN IRON SHIP. 305 



TMs force is resolvable into two others, the horizontal 8 H, and 

 the vertical 8Z; and the former is further divisible into SB, 

 parallel to the midship line, and B H, transverse to it. 



The magnetic power of the bar is thus resolved parallel to the 



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. 



VOL. XXXIT. 20 



