MAGNETISM AND ELECTRICITY 



405 



FIG. 225 



pillar, and then bent downwards in the middle between. The 

 little trough of iron filings can be lifted up first, before the 

 current passes, with no result ; afterwards the filings will 

 adhere, and show an evident tendency to range themselves at 

 right angles to the 

 current. 



To explain the 

 construction of an 

 electro-magnet, two 

 small solenoids of 

 insulated wire are 

 arranged across a 

 small frame as in 

 fig. 226, being wound in contrary directions. They should 

 be wound so much apart that the turns can be clearly seen. 

 A stout needle may be first introduced into each, and a mag- 

 netised needle, sus- 

 pended at one end 

 by a thread, may be 

 shown to be equally 

 attracted by either ; 

 then on passing the 

 current, it will be 

 attracted by one and 

 repelled by the other 

 as shown in the 

 figure. Withdraw- 

 ing the needles, and 

 introducing a small 

 horse-shoe of an- 

 nealed iron wire (fig. 227), we have an electro -magnet, whoso 

 whole construction is clearly seen, and which will support a 

 nail or other piece of iron easily. 



Magnetic hysteresis can be shown by any electro-magnet 

 small enough for the field of the lantern, or by a larger one 



PIG. 226 



