232 Our Surroundings 



the current passes. This arc becomes very hot. It produces one 

 of the highest temperatures man has ever succeeded in obtaining. 

 With this high temperature comes a very brilliant light. This 

 method of lighting is both expensive and hard to control. In 

 consequence, it is rapidly being replaced by the electric bulb. 



The Incandescent Lamp. The incandescent lamp, or 

 electric bulb, was invented by Thomas Edison. It is a glass 

 bulb from which the air has been extracted and in which is a 

 fine filament or wire. When an electric current passes through 

 this filament it becomes very hot on account of the resistance 

 it offers and as a result the filament gives off a brilliant light. 



In the first incandescent 

 light, air was extracted from 

 \ the bulb, leaving a vacuum. 



This was done because other- 

 wise the oxygen in the air 

 would unite with the filament 

 at the high temperature to 

 which it must be heated. This 

 would ruin the bulb. Later it 



General Electric Company. Brown Brothers. 



INCANDESCENT LAMPS was found lhat the Quality of 



Edison's First Sue- An Improved the bulb COUld be improved 



cessful Lamp. Lamp. 



by filling it with some gas 



that would not unite with the filament. Nitrogen seemed to 

 be the best gas, so the nitrogen bulb began to be used. Now, 

 according to their uses, bulbs are filled with different gases, such 

 as nitrogen, argon, neon or helium. Bulbs of special design are now 

 used in heating, in scientific, and in radio apparatus. The tubes 

 which form the letters of some electric signs are filled with neon. 

 As an electric current passes through the tube, the gas glows. 



Fuses. It sometimes happens that two electric wires in a 

 house become crossed at a point where the insulation is worn 

 away. Since electricity follows the path of least resistance, the 

 current jumps from one wire to the other at this point rather 

 than go around the circuit where the resistance is greater. This 

 shortening of the circuit greatly increases the current and the wire 

 becomes hotter until it may start a fire. 



