HEAT AND LIGHT FROM ELECTRICITY 93 



tion. Again use the stored energy to ring the bell. Repeat 

 several .times, each time reversing the charging. Does the 

 bell ring longer ? Examine the lead plates and give a reason. 



67. HEAT AND LIGHT FROM ELECTRICITY 



Whenever electricity passes through a substance, it meets 

 with more or less resistance, according to the material. Wher- 

 ever there is resistance, heat is produced. The incandescent 

 lamp is an example of heat, as well as light, being produced by 

 electricity. Very often fires have been caused by overheated 

 electric wires. In nearly every circuit, however, there is 

 inserted a piece of wire of low melting point, which melts 

 when an excessive current passes, and thus protects the rest 

 of the circuit. 



References : 



1. 1803:305-311. Heat and Light from Electricity, 



a. 1801 : 400-403. The Electric Light. 



6. 1804 : 587-593. The Electric Light. 



c. 1805 : 456-462. Heat Effects of Electricity. 



d. 1807 : 385-388. Heat, Light, and Power from Electric 



Currents. 



e. 1808 : 305-306. Heating Effects of the Electric Current. 

 /. 1808 : 363-365. Electric Lighting. 



g. 1809 : 445-451. Heat and Light from Electricity. 



h. 1811 : 317-318. The Incandescent Lamp and the Arc Light. 



Experiment 32. Heat and Light from Electricity. 



Apparatus : Two or three dry cells, or a storage cell, German 

 silver wire No. 30, iron wire No. 30, file. 



a. Connect the cells in series and pass the current through 

 an inch of the fine wire. Note the rapidly increasing tem- 

 perature and the light which is produced. Iron melts at 

 about 2200 Fahrenheit. What do you think about the pro- 



