TERRESTRIAL MAGNETISM, ETC. 251 



thing like a concentration of magnetic action. In 

 respect to bar magnets, or magnetic needles, I shall 



FIG. 34. Curved lines of force. 



use the term " north pole " in a perfectly definite 

 sense to signify a certain " centre of gravity " of 

 northern polarity, and the term " south pole " to 



