MAGNETS. 



191 



an astatic needle (Fig. 129). An astatic 

 needle assumes no particular direction 

 with respect to the earth. ( 391.) 



315. Terrestrial Magnet- 

 ism. If a small dipping needle be 

 placed over the end of a bar mag- 

 net, the needle will take a vertical 

 position with its -f end down (Fig. 

 130). As the needle is moved toward the other end of the 

 bar it turns from its vertical position. When over the 



FIG. 129. 



FIG. 130. 



neutral line, the needle is horizontal. As it approaches the 

 + end of the magnet the needle again becomes vertical, 

 but the end of the needle is drawn down. If a dipping 

 needle be carried from far southern to far northern lati- 

 tudes it will act in a similar way. These facts seem to 

 teach that the earth is a great magnet with magnetic 

 poles near its geographical poles. The magnetic pole 

 in the northern hemisphere was found in 1832 by Capt. 

 Ross. It is a little north and west of Hudson's Bay, in 

 latitude 70 05' N., and longitude 96 45' W. A place in 

 the southern hemisphere has been found where the needle 

 is nearly vertical. 



316. The Earth's Inductive Influence. That 



the earth is really a magnet is further shown by its indue- 



