MAGNETISM AND ELECTRICITY 



169 



having properties of its own, but obeying laws corresponding 

 quite closely to those governing the motion of water. A 

 great many explanations can be offered by comparing the 

 action of electricity with water. For example, electricity 

 flows through a wire in much the same way as water flows 

 through a pipe. From their likeness it has become popular 

 to speak of electricity as " juice." 



Since electricity is, in a sense, considered a fluid, its flow 

 is called a current, and any substance, such as copper wire, 

 through which it flows is called a conductor. All metals, 

 salts, and solutions, living vegetable substances, and water, 

 are conductors of electricity. There are some bodies, how- 

 ever, such as glass and rubber, that offer a resistance so 

 great as to prevent the passage of electricity. Most vege- 

 table substances in a dry state, such 

 as shellac, resin, rubber, paper, and 

 cotton are in this group. Other 

 non-conductors are wood, sulphur, 

 glass, mica, silk, porcelain, and oil. 

 The path through which a current 

 passes is called a circuit. When a 

 path is continuous it is called a closed 

 circuit, but when there is a break it 

 is called an open circuit. 



200. Relation of Magnetism to 

 Electricity. If a piece of copper wire 

 through which a current of electricity 

 is flowing is passed through a cardboard 

 or glass plate and the card or plate is 



sprinkled with iron filings, the filings arrange themselves in circular 

 lines (Fig. 71). If the card or plate is jarred and the iron filings 

 displaced, they will rearrange themselves in the same circular lines. 



FIG. 71. Lines of Mag- 

 netic Force Around an 

 Electric Wire. 



