192 



MAGNETS. 



tive influence. An iron bar placed in the position 

 assumed by the dipping needle and struck a sharp 

 blow on the end becomes polarized. The magnetic in- 

 fluence of the bar may be tested by moving a small mag- 

 netic needle along its length, and noticing that one end of 

 the bar attracts one end of the needle and the other the 

 other end. A steel poker which has usually stood in a 

 nearly vertical position may thus be shown to have ac- 

 quired magnetism. 



317. Names of Magnetic Poles. We have now learned 

 to regard the earth as a huge magnet, with one pole in the northern 

 hemisphere and one in the southern Since unlike poles attract 

 each other, it follows that the earth's magnetic pole situated in the 

 northern hemisphere is opposite to the end of a magnetic needle that 

 points to the north. From this fact, great confusion of nomencla- 

 ture has arisen. We have spoken of the end of the needle that 

 points north as or negative. Following this nomenclature, the 

 northern magnetic pole of the earth must be + or positive. (See 

 Report of the British As- 

 sociation Committee on 

 Electrical Standards, Ap- 

 pendix C, 1863.) But 

 popular usage calls the 

 north-seeking end of the 

 needle the north pole, 

 and the other end the 

 south pole. This intro- 

 duces great confusion 

 when we wish to speak 

 of the magnetic poles of 

 the earth. The nomen- 

 clature that we have 

 adopted obviates this 

 confusion. 



318. Inclina- 

 tion or Dip. 



The angle that a 



FIG. 131. 



