SECT. XXX. THE DIP. 301 



and about 162 east longitude. The position of the 

 other south magnetic pole, if it exists, is unknown. 



In consequence of the attraction and repulsion of 

 these poles, a needle suspended so as to move freely in 

 a horizontal direction, whether it be magnetic or not, 

 only remains in equilibrio when in the magnetic meridian, 

 that is, when it is .in a place which passes through a 

 north and a south magnetic pole. In some places the 

 magnetic meridian coincides with the terrestrial me- 

 ridian, and m these a magnetic needle freely suspended, 

 as in T;he mariner's 'compass, points to the true north ; 

 but if it be carried successively to different places on 

 the earth's surface its direction will deviate, sometimes 

 to the east, and sometimes to the west of the true north. 

 Imaginary lines drawn on the globe through all the 

 places where the needle points due north and south are 

 called lines of no variation. Imaginary lines drawn 

 through all those places whore the needle deviates from 

 the geographical meridian by an equal quantity, are lines 

 of equal variation. 



A magnetic needle suspended so as to be movable 

 only in a vertical plane dips, or becomes more and more 

 inclined to the horizon the nearer it is brought to a 

 magnetic pole, and there it becomes vertical. Lines 

 of equal dip are such as may be imagined to pass 

 through all those points on the globe where the dipping 

 needle makes the same angle with the horizon. In 

 some places the dipping needle becomes horizontal, and 

 there the influences of the north and south poles are 

 balanced, and an imaginary line passing through all such 

 places is the magnetic equator. In going north from 

 the magnetic equator one end of the dipping needle dips 

 more and more till it becomes perpendicular at the 

 north magnetic pole, while in proceeding south from 

 the magnetic equator the other end of the dipping 

 needle dips, and at last becomes perpendicular at the 

 south magnetic pole. The magnetic equator does not 

 coincide with the terrestrial equator : it appears to be 

 an irregular curve passing round the earth, inclined 

 to the earth's equator at an angle of about 12, and 

 crossing it in several points, the position of which seems 

 stiU to be uncertain. According to some accounts, three 

 Cc 



