7 6 



ELEMENTS OF ELECTRICITY AND MAGNETISM. 



very strongly. This is shown very strikingly by passing the flat 

 end of a magnet pole over a table on which a very few iron filings 

 have been placed, the filings are all caught by the corners of the 

 pole. 



The lines of force in the neighborhood of a sharp-pointed mag- 

 net pole diverge very greatly indeed as shown in Fig. 4 1 , that is 

 to say, the magnetic field in the neighborhood of the point is non- 

 uniform to a high degree, and 

 such a magnet pole has a 

 strong attraction for small 

 particles of magnetic material. 

 A pointed magnet pole is an 

 essential feature of the mag- 



j MIXED 

 MATERIAL 



NON-MAGNETIC 

 MATERIAL 



Fig. 42. 



netic ore separator, the action 

 of which is shown in Fig. 42. 

 The crushed ore falls in a thin 

 stream before a pointed, or 

 wedge-shaped, magnet pole. 

 The particles of magnetic material are attracted by the pointed 

 pole and thus deflected, while the non-magnetic material falls 

 straight downwards. 



Surgeons sometimes make use of a pointed magnet for remov- 

 ing particles of iron or steel from the eye. ' 



44. Tension and energy of the magnetic field. Consider the 

 opposite poles of two magnets as shown in Fig. 43. Their force 

 of attraction is due to the tension of the magnetic field, the ten- 

 sion of the lines of force as it is sometimes called. The lines of 

 force of the magnetic field also push each other apart side wise. 

 This sidewise push of the lines of force on each other is evident if 

 we consider that the lines of force in Fig. 43 are curved so that 

 they must exert a side force if they are under tension. 



When the two magnet poles in Fig. 43 are allowed to move 

 nearer together, their force of attraction does mechanical work, 

 and the mechanical work thus obtained comes from the magnetic 

 field ; that is to say, a magnetic field represents a store of energy, 



