480 MAGNETISM AND ELECTRICITY 



directions, dependent upon their mutual attraction ; and thus 

 they neutralize one another. When the bar becomes mag- 

 netized the molecules tend to arrange themselves so that 

 like poles lie in the same direction (Figure 

 152). When the magnet is heated or jarred the 

 molecules are moved out of this alignment and 

 the magnetism is weakened. 



BBBG 

 BBBB 

 BB-B 

 HBHG 

 HBHH 

 BHBB 

 BBiB 

 BBBB 

 BBBB 

 BBBB 

 BBBB 

 BBBB 

 BBBB 



Electricity by Friction. It was known by the 

 ancient Greeks that when certain substances, 

 one of which was amber, were rubbed, they 

 had the power of attracting light objects. This 

 property was afterward called electricity, from 

 FIGURE 152 the Greek word for amber. 



Experiment 152. Place some small pieces of paper or pith balls 

 on a table and after rubbing a glass rod with silk bring it near the 

 pieces. Do the same with a stick of sealing wax or a hard rubber 

 rod rubbed with flannel or a cat's skin. Note the action of the 

 pieces. 



Experiment 163. Rub a glass rod briskly with silk and place in 

 a wire sling such as was used in Experiment 148. Bring toward one 

 end of the glass rod another glass rod which has been rubbed with 

 silk. Do the rods attract or repel each other? Bring toward the 

 suspended rod a piece of sealing wax or a vulcanite rod which has 

 been rubbed with flannel or a cat's skin. Does this repel or at- 

 tract the glass rod? 



Experiment 154. Suspend a pith ball by a silk thread from the 

 ring of a ringstand. Rub a glass rod with a piece of silk and bring 

 it near the pith ball but do not allow the two to touch. Note the 

 action of the ball. Touch the pith ball with the rod. Does it 

 behave now as it did before? Rub a vulcanite rod with a piece of 

 flannel or cat's skin and bring it near a suspended pith ball. Does 

 the pith ball act as it did with the glass rod? Touch the pith ball 

 with the rod. How does it act? Bring a glass rod rubbed with 

 silk near a pith ball which has been in contact with a vulcanite rod 



