chap, ix.j MAGNETIC NEEDLE. 93 



times with one pole of a strong magnet held in a 

 sloping direction, moving always in the same direction, 

 from one end to the other of the bar, the end touched 

 last forming the pole opposite to that of the influencing 

 magnet used (2) by separate touch, i.e. by using two 

 magnets of equal strength, placing opposite poles in 

 contact with the bar at the middle and moving them, 

 both at the same time, away from one another to 

 opposite ends, repeating the manoeuvre several times ; 

 (3) by double touch, i.e. by placing the opposite poles of 

 two magnets, separated by a piece of wood in the 

 middle of the bar, and moving them together to one 

 end, then from this to the other end, and from it back 

 to the middle. The method most frequently used is 

 by drawing the bar over the opposite poles of a strong 

 electro-magnet in opposite directions. 



Strong magnets are formed of several bars, shaped 

 like a horse-shoe, bound together, like poles being 

 placed together. Suppose two bars equally strongly 

 magnetised are placed together, so that unlike poles 

 are in contact, then the magnetism of the one neu- 

 tralises that of the other, and the result is loss of all 

 magnetism so long as they remain in contact. There- 

 fore, for forming a MAGNETIC MAGAZINE or BATTERY, as 

 it is called, like poles are placed in contact. The 

 strength of such a magnet is found to be preserved 

 by placing across from one pole to the other a piece 

 of soft iron, called a KEEPER, or ARMATURE. This 

 reacts inductively on the poles, and so preserves their 

 magnetism and even increases it. 



Inclination or dip. Tf a magnet be suspended 

 so that it is free to move both horizontally and ver- 

 tically, it not only points north and south, but one 

 end is found to dip down. This is the inclination of 

 the magnet. In the northern hemisphere it is down 

 towards the north, and vice versa. 



A magnetic needle is usually in the form of 



