178 TERRESTRIAL PHENOMENA. 



of magnetic latitude: near the equator, in the Island of Rawak, 

 for example, they barely amount to three or four minutes, 

 while in middle Europe they attain to thirteen or fourteen 

 minutes. Throughout the northern hemisphere the move- 

 ment of the north end of the needle from 8 A.M. to 1-' P.M. 

 or thereabouts, is from east to west ; and, as at the same hours 

 n the southern hemisphere, the same end of the needle 

 moves in the opposite direction, or from east to west, atten- 

 tion has been justly called ( 153 ) to the presumption, that 

 there must be a region of the earth, probably between the 

 terrestrial and magnetic equators, in which no horary varia- 

 tion of the declination is sensible. This fourth curve, which 

 might be called the curve of no motion, or line of no horary 

 variation of the declination, has not yet been found. 



The name of magnetic poles has been applied to those 

 points on the Earth's surface where the horizontal force 

 disappears, and to these points more importance has been at- 

 tached than properly belongs to them; ( 154 ) in like manner 

 the curve on which the needle has no inclination, but rests 

 in a horizontal direction, has been called the magnetic 

 equator. The position of this li]ie, and its secular change 

 of form, have of late years been objects of careful investiga- 

 tion. According to the excellent memoir of Duperrey ( 155 ), 

 who crossed the magnetic equator six times between 1822 

 and 1825, the nodes or intersection of the two equators, or 

 the two points at wlu'ch the line without inclination crosses 

 the geographical equator and passes from one hemisphere 

 into the other, are unequally distributed; in 1825, the node 

 near the Island of St. Thomas on the "West Coast of Africa, 

 was 188 from the node in the Pacific, which is near the 

 small islands called Gilbert Islands (nearly in the meridian 



