NAVIGATION. 21 



magnetic axis, is in a particular direction de- 

 pending on the particular locality in which the 

 experiment is made. This direction is actually 

 shown by the " dipping needle." The ordinary 

 horizontal needle tends to dip into the same 

 direction, but is prevented by a counterpoise 

 adjusted to keep it horizontal. The dipping 

 needle is vertical at the two magnetic poles, and 

 there the horizontal needle shows no direction. 

 Early Arctic navigators imagined the magnetic 

 virtue to be impaired by cold, when they found 

 their compasses becoming sluggish as they ap- 

 proached the north magnetic pole ; but the 

 dipping needle disproves this idea by vibrating 

 actually with greater energy, rather than with less, 

 in polar regions. The charts (Figs. 5 and 6) before 

 you explain sufficiently how the magnetic north 

 and south line lies in any part of the world. 



19. The lines on these diagrams show what 

 Faraday would have called the lines of horizontal 

 magnetic force. They are sometimes called 

 magnetic meridians. All these curved magnetic 

 north and south lines pass through two points 



