84 INTRODUCTION TO GENERAL SCIENCE 



The reason that electricity produces magnetism in a piece of 

 iron is because there is magnetism around every wire carry- 

 ing an electric current. Magnetism is induced in the iron. 

 This effect is made use of in the electromagnet, bell, tele- 

 phone, telegraph, motor, and dynamo, as well as in many 

 toys. 

 References : 



1. 1803:227-234. Magnetism. 



2. 1803:261-262. Electricity in Motion Produces Mag- 



netism. 



a. 1801 : 300-310. Magnetism. 



6. 1802 : 368-378. Magnetic Effect of the Electric Current. 



c. 1804:523-530. Magnetism. 



d. 1805:369-380. Magnetism. 



e. 1806:429-439. Magnetism. 

 /. 1807:339-352. Magnetism. 

 g. 1808:248-264. Magnetism. 

 h. 1809:359-373. Magnetism. 



Experiment 27. Magnetism. 



Apparatus : Two bar magnets six inches long, piece of quar- 

 ter-inch iron rod (large nail), thirty feet of double cotton- 

 covered copper wire No. 20, dry cell, bits of wood, brass, iron 

 nail, silk thread. 



a. Suspend one magnet at its middle point by a silk thread, 

 and balance it. If the thread is allowed to untwist, the mag- 

 net may point to the north. Approach in succession the two 

 ends of the other magnet. The similar poles are marked. 

 Write out the laws of attraction and repulsion. Do the 

 magnets have to obey these laws ? 



b. Wind about thirty feet of insulated wire on the large 

 nail, trying to imitate the winding of thread upon a spool. 

 Note that there is no magnetism in the iron. Attach the two 

 ends of the wire to the connecting screws of the dry cell. Can 



