CHAPTER XXIII 



MODERN ELECTRICAL INVENTIONS 



An electric current acts like a magnet. In order to under- 

 stand the action of the electric bell, we must consider a third 

 effect which an electric current can cause. Connect some cells 

 as shown in Figure 75 and close the circuit through a stout 

 heavy copper wire, dipping a portion 

 of the wire into fine iron filings. A 

 thick cluster of filings adheres to the 

 wire (Fig. 84), and continues to cling 

 to it as long as the current flows. If 

 the current is broken, the filings fall FlG * 84.- A wire carding current 



' attracts iron filings. 



from the wire, and only as long as the 



current flows through the wire does the wire have power to 

 attract iron filings. An electric current makes a wire equivalent 

 to a magnet, giving it the power to attract iron filings. 



Although such a straight current-bearing wire attracts iron 

 filings, its power of attraction is very small. But its magnetic 



strength can be increased 

 by coiling as in Figure 



FIG. 85. - A loosely wound coil of wire. 8 5' Such an . arrange- 

 ment of wire is known 



as a helix or solenoid, and is capable of lifting or pulling larger 



and more numerous filings and even good-sized pieces of iron, 



' such as tacks. Filings do not adhere to the sides of the helix, 



but they cling in clusters to the ends of the coil. This shows 



, that the ends of the helix have magnetic power but that the 



sides have not. 



217 



