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THE POPULAR SCIENCE MONTHLY 



eral magnetic features of a ship built head north, only that now the 

 north magnetism predominates on the starboard side, and south 

 magnetism on the port side. Finally, in Fig. 12, ship's head south- 

 west, we have the general features of the ship's head south, but 

 with the neutral line taking a more horizontal trend, and the south 



STARBOARD SIDE 



SHIPS HEAD MAGNmC N.ff. 



ship's li£AD MA5WET1C S.W. 



Pigs. 9, 10, 11, and 12.— The Varied Magnetic Featuees op Iron Ships, due to the Direction 

 OP their Heads while building. 



polarity lessened on the starboard side and increased on the port 

 side. And all the above is in close conformity to what theory 

 requires. 



The means taken for discovering the permanent magnetic 

 character a ship has acquired in building, are a dock -survey, 

 shown in Figs. 13 and 14. To simplify the exj)lanation, let us 

 suppose the ship and dock to lie parallel to the magnetic meridian. 

 Stations numbered 1, 2, 3, etc., are established on the different 

 steps of the dock, and the distance that each is from the line A, B 

 and also from the ship's side is measured. A compass is taken 

 successively to each station, and the direction in which its needle 

 points is noted. Of course, if no disturbing mass were near, it 



