210 THE OCEAN. [Book IX. 



tendency of magnetism is to turn the positive end — 

 that is, what is commonly called the north pole of 

 the needle — in the direction of the earth's motion ; 

 that is to say, in the direction of the South Pole, or 

 thereabouts. And, as in the ocean, lines of lesser 

 force are overwhelmed by lines of greater force, so 

 that currents are caused to run along the lines of 

 lesser force in the opposite direction to that in which 

 the force which impels them acts ; so also must the 

 northward direction of the magnetic-needle result 

 from the overwhelmmg of lines of lesser magnetic 

 force by those of greater force ; that is to say, the 

 lines of magnetic force must run through the central 

 parts of the earth from the north to the south mag- 

 netic pole, and then spread out over the surface of 

 the earth towards the equator, crossing which, they 

 must converge again towards the north magnetic 

 pole ; so that the lines of greatest force, running 

 through the central parts of the earth, overwhelm 

 the lines of lesser force on the surface of the earth ; 

 thus causing the needle, when placed in the lines of 

 lesser force, to point in the opposite direction to that 

 in which magnetism acts ; and, at the north magnetic 

 pole, being in the line of greatest force, to point down 

 through the central parts of the earth to the South 

 Pole ; and, at the south magnetic pole, to point right 

 away into space, marking the point in space towards 

 which the earth may be moving. 



Then, by the magnetic action which we have 



