USES OF ELECTRICAL ENERGY 



167 



current, in passing through the water, acts upon the salt 

 so as to set free the metal that it contains. This metal, 



FIG. 123 



in tiny particles, gathers about the solid bodies through 

 which the current leaves the liquid, thus covering those 

 articles with a metal coating. The current is commonly 

 furnished by a dynamo, though a battery 

 of cells may be used in experiments. 



192. Electric Lights Electric lights 



depend upon the thermal effect of elec- 

 trical energy. A current is made to pass 

 through a poor conductor against great 

 resistance ; in doing this, it heats the con- 

 ductor until it is luminous. Two sorts of 

 lamps are common, incandescent and 

 arc lamps. 



Fig. 124 shows the familiar bulb of 

 an incandescent light. The fine thread of 

 carbon inside the bulb offers great resist- 

 ance to the current that is sent through it. 

 Thus the carbon thread becomes very hot and luminous. 

 The space within the glass bulb is a nearly perfect 



FIG. 124 



