168 MAGNETISM 



interposed. There is, however, one striking exception. If the 

 screen is iron and is of sufficient extent the deflection diminishes, 

 the action of the magnet being screened off by the iron from the 

 space beyond. 



Induced Magnetisation. A piece of iron brought into 

 contact with a magnet becomes itself a magnet by induction, the iron 

 being magnetised in such a manner that the end of it in contact 

 with the magnet is a pole of the kind opposite to that with which 



it is in contact, while the other 

 end of the iron is a pole of the 

 same kind. The adherence of the 

 iron to the magnet is explained 

 by the formation of the unlike 

 pole, while the existence of the 

 like pole at the further end may 

 easily be tested by means of a 

 suspended compass needle. 



Several pieces of iron may 

 thus be hung one below the other 

 from a magnet pole, each mag- 

 netising the next below it, unlike 

 poles being together and the lasi 

 pole being like the inducing pole 

 of the magnet, as in I-'ig. 112. 

 The NSP of the last piece of iron 

 ivpeK the NSP of a needle. 



77//.V magnetisation ant take />/<ur 



without contact, a given pole inducing a pole of the opposite kind to 

 itself in the nearer part of the piece of iron in which the induction 

 occurs, the further part having a pole of the same kind. This niav 

 be shown by placing a compass needle near one end of a bar of iron 

 and then bringing a magnet up near the other end, as in Fig. ll!j, 

 say with the NSP towards the bar: the NSP of the needle is re- 

 pelled, showing that a NSP is induced in the part of the bar more 



FIG. 112. 



N 



S N 



Bat- of Jr-cn \ Mtxt/rt<-r 



FIG. 113. 



distant from the magnet. If the compass be moved along a line 

 parallel and near to the bar it will be found that the NSP is 

 attracted by the part of the bar nearer to the inducing magnet, 

 which is therefore a SSP. 



If we bring a piece of unmagnetised iron near a compass needle, 

 either end of, the needle is attracted. This is an example of 



