260 



GENERAL SCIENCE 



CURRENT THROUGH 



THE HELIX 

 Affects the compass. 



come out is the north pole. This can be proved by 

 holding the compass at either side and observing which 

 pole of the needle is attracted. 



Wind a wire around a pencil like the threads on a 

 _ screw. Remove the pencil and con- 



nect the ends of the wire forming 

 the coil, commonly called a helix, 

 with a good electric cell. Hold one 

 end of the helix near a suspended 

 magnet or compass needle. (See 

 illustration.) The helix will act in 

 every respect like a magnet, with an N pole at one end 

 and an S pole at the other. By reversing the helix and 

 pointing it at the N pole of a compass needle each time, 

 we can easily find which is the N pole of the helix and 

 which end is the S pole. 

 The magnetic lines of force 

 go into the 5 pole end of 

 the helix and come out of 

 the N pole end. If the 

 current goes around the 

 helix in the right-hand- 

 screw direction, the magnetic lines of force go through 

 the helix in the same direction that the current goes 

 from one end to the other. By reversing the current 

 the lines of force will also reverse. 



181. The Electromagnet. The 

 helix is a form of electromagnet. 

 By inserting in the helix an iron 

 rod which will serve to conduct 



the magnetic lines of force, the effect upon the compass 

 needle is much more evident. The iron rod will also 

 pick up iron filings. By doubling the number of turns 



FIELD ABOUT A HELIX 



HELIX WITH CORE 



