MAGNETISM. 4«09 



degrees ; the ends G and I of the bars are to be 

 separated two or three tenths of an inch from eacli 

 other. Keeping the bars in his position, move 

 them slowly over the bar AB, from one end to the 

 other, going from end to end about fifteen times. 

 Having done this, change the poles of the bars 

 (i.e. the marked end of one is always to be against 

 the unmarked end of the other), and repeat the 

 same operation on the bar CD, and then on the 

 opposite faces of the bars. The touch thus com- 

 municated may be further increased, by rubbing 

 the different faces of the bars with sets of magnetic 

 bars, disposed as in Fig. 18. 



In these operations all the pieces should be well 

 polished, the sides and ends made quite flat, and 

 the angles quite square. 



A magnet, bent so that the two ends almost 

 meet, is called a horse-shoe magnet. To render 

 it magnetic, place a pair of magnetic bars against 

 the ends of the horse-shoe, with the south end of 

 the bar against that of the horse-shoe which is in- 

 tended to be the north, and the north end of the 

 bar to that which is to be the south : the contact, 

 or lifter of soft iron, to be placed at the other end 

 of the bars. Also rub the surfaces of the horse- 

 shoe with a pair of bars placed in the form of a 

 compass, or with another horse-shoe magnet, turn- 

 ing the poles properly to the poles of the horse- 

 shoe magnet ; being careful that these bars never 

 touch the ends of the straight bars. If the bars 

 are separated suddenly from the horse-shoe mag- 

 net, its force will be considerably diminished : to 

 prevent this, slip on the lifter, or support, to the 

 end of the horse-shoe magnet, but in such a man- 

 Her, however, that it may not touch the bars ; the 



