MAGNETISM. 105 



it, and will place itself in the same straight line 

 with the axis of the large magnet. 



This simple experiment will enable the reader to 

 comprehend easily the phenomena of the magnetic 

 inclination, or of the dipping needle, upon the 

 surface of the earth ; for it is only necessary to 

 imagine that the earth is a large magnet (as in fact 

 it appears to be), and that any magnet, or magne- 

 tic needle commonly used, is the small magnet 

 employed in the above-mentioned experiment ; for, 

 supposing that the north pole of the earth is pos- 

 sessed of a south magnetic polarity, and that the 

 opposite pole is possessed of a north magnetic po- 

 larity, it appears evident, and it is confirmed by 

 actual experience, that when a magnet, or mag- 

 netic needle, properly shaped and suspended, is 

 kept near the equator of the earth, or, more 

 properly speaking, near the magnetic equator of 

 the earth (since neither the magnetic equator, 

 nor the magnetic poles of the earth, coincide 

 with its real equator and poles), it must remain in 

 an horizontal situation : if the magnet be removed 

 nearer to one of the magnetic poles of the earth, 

 it must incline to one of its extremities namely, 

 that which is possessed of the contrary polarity ; 

 and this inclination must increase in proportion as 

 the needle recedes from the magnetic equator of 

 the earth. Lastly, when the needle is brought 

 exactly over one of the magnetic poles of the 

 earth, it must stand perpendicular to the horizon 

 of that place. 



The directive property and dipping of the needle 

 upon the surface of the earth is exactly analogous 

 to that of a small magnet upon the surface of a 

 small globe, having a magnet inclosed within it, 

 which apparatus is called a terretta. 



n n 3 



