270 POPULAR LECTURES AND ADDRESSES. 



northern one was actually reached and passed by 

 Parry and other Arctic navigators ; and the southern 

 one was so nearly reached by Sir James Ross's Ant- 

 arctic expedition of 1840 41, that there can be no 

 doubt of there being a south magnetic pole not far 

 from the position marked. But the question 

 whether or not there are other poles, whether north 

 or south, besides those marked cannot be quite 

 decisively answered without more of observation, in 

 the Arctic and Antarctic regions, than has hitherto 

 been made. If there are really two north magnetic 

 poles of convergence of the directional lines, there 

 must, as shown by Gauss, be also a third pole, where 

 the ordinary mariner's compass would show no 

 directional tendency, and where the dipping needle 

 would point with its true south pole vertically 

 downwards. There would be no convergence of 

 the directional lines to this intermediate pole, which 

 might be called a pole of avoidance rather than a 

 pole of convergence. 



Even should it turn out that there is only one 

 north and one south magnetic pole now, it by no 

 means follows that there may not have been at 



