QUALITY OF THE EAKTH's MAGNETISM. 



13 



respectively red and blue poles, exactly similar to those 

 of a straight bar-magnet. 



11. The action of the Earth is exactly the same as 

 that of a large magnet, whose red end is on the south 

 side and whose lime end is on the north side. For 

 experimental purposes, the Earth's action may be neu- 

 tralized over a large space. Or its action on a special 

 magnet may be rendered insensible by use of the astatic 



needle. 



Fig. 3. 



JUT 



In Figure 3, suppose the needle A to be turning 

 freely on a fine point and the magnet B to be delicately 

 suspended above it, both magnets taking the position 

 given to them by the Earth's magnetic power, and 

 therefore parallel, with their red ends pointing to the 

 north. In this state, the needle A is maintained vigor- 



