190 



MAGNETS. 



FIG. 126. 



poles near each other, their combined effect on the iron 

 filings may be easily observed. 



314. Magnetic Needles. A 



bar magnet may be supported by 

 balancing it upon a pivot, by sus- 

 pending it by a fine untwisted thread, 

 by floating it upon water by means 

 of a cork, and in several other ways. 

 *4. small bar magnet suspended FIG. 127. 



in such a manner as to 

 allow it to assume its cho- 

 sen position is a magnetic 

 needle. (See Appendix J.) 



(.) If it be free to move in c. 

 horizontal plane it is a horizontal 

 needle ; e. g. , the mariner's or the 

 surveyor's compass (Fig. 127). It 

 will come to rest pointing nearlv 

 north and south. If the magnet be 

 free to move in a vertical plane it 

 constitutes a vertical or dipping 

 needle (Fig. 128). Two magnets 

 fastened to a common axis but hav- 

 ing their poles reversed constitute 



FIG. 128. 



