94 ON MAGNETISM. 



was 67 56'. Adopting as elements of calculation that 

 in 1848 the dip and horizontal force were 68 47' and 

 376, and, in 1866, 68 V and 3'85 : the total force was, 

 in 1848, 10*39, and, in 1866, 10'28 (in English units), 

 or 4'791 and 4'740 (in Metrical units). 



42. Reference to the points of principal interest in 

 Figures 20, 21, 28, 29, 35, 36: secular change in the place 

 of North Magnetic Pole. 



Before entering upon the consideration of the dia- 

 grams, we will allude to some general points regarding 

 the connexion of the magnetic meridians with the curves 

 of equal dip and of equal horizontal force. 



Adopting, as the most convenient definition of 

 " Magnetic Pole," (when not qualified by any other 

 words), " the point where the dip is vertical," there is 

 no reason in nature why there should not be more than 

 one magnetic pole in the north (or in the south). If, at 

 one of these proximate places, the red pole dips, and at 

 the other the blue pole dips, there must be between 

 them a place of no dip (in the same manner as, in 

 Figure 37, there is a place of no dip between the north 

 and south poles of vertical dip with opposite poles of 

 the needle). But, if the red pole dips at both, there is 

 some complication introduced into the forms of the 

 equal-dip curves. We will however commend these to 

 the examination of the speculative student : remarking 

 that we have no reason to think that there is more than 

 one Magnetic Pole or place of vertical dip either in the 

 north or in the south. 



