ELECTRIC LIGHT 



Positive 



ELECTRIC LIGHT 



Dynamo 



Dynamo 



ELECTRIC LIGHTS IN A CIRCUIT 

 Multiple connection of incandescent lamps, three-wire system. 



would last only a fraction of a second, for car- 

 bon burns in air. If carbon were used it would 

 have to be enclosed in a vacuum, so that it 

 could not burn. 



The Carbon Lamp. It was Edison who in 

 1879 devised the first successful carbon filament 

 lamp. This lamp consisted of a thread of 

 carbon in a sealed glass globe from which the 

 air had been pumped until only about a 

 millionth part of the original air remained. 

 Edison at first tried to make the thread of 

 carbon by charring cotton thread, paper, wood 

 everything, in fact, that could be adapted 

 to the purpose. Bamboo fiber was among the 

 substances tried. It proved superior to the 

 other materials and he began a search for the 

 best form of bamboo. Men were sent to all 

 parts of the world where bamboo grows and 

 at the risk of their lives secured specimens of 

 every known variety. The search cost about 

 $100,000, and resulted in the adoption of a 

 Japanese variety. 



For a number of years the carbonized fiber 

 of the bamboo was used and then replaced by 

 the "squirted" filament. Such a filament is 

 made by "squirting" a solution of . cellulose 

 through glass jets into alcohol. The alcohol 

 hardens, that is, it coagulates, the cellulose, 

 and this is afterwards carbonized by heat. The 

 ends of the carbon filament are soldered to two 

 platinum wires which are sealed into the glass 

 and make connection with the electric current. 



The Tungsten Lamp. This is in some re- 

 spects superior to the carbon lamp. The tung- 

 sten filament when prepared by the "squirting" 

 process was so fragile that the lamp could not 

 be used where it would be jarred; but since 

 the discovery of a wire-drawing process of 

 preparing the filament tungsten lamps have 

 been made of such durability as to make them 



suitable for use even in street cars. The great 

 advantage of the tungsten lamp is its high 

 efficiency. A tungsten lamp gives out about 

 one candle power of light for every one and 

 one-fourth watts of electrical power which it 

 consumes, while a carbon filament lamp yields 

 only about one can- 

 dle power for every 

 three and one-half 

 watts. For .the 

 same amount of 

 light, therefore, the 

 cost is nearly three 

 times as much when 

 using the carbon 

 lamp as when using 

 the tungsten lamp. 



The Nitrogen 

 Lamp. A recent in- 

 vention is an incan- 

 descent lamp filled 

 with nitrogen. This 

 is the most efficient 

 lamp yet devised, 

 for it furnishes more 

 light for a given 

 amount of electrical 

 energy than any 

 other electric light. 

 A 2,000-candle-power 

 lamp requires only P 

 1,000 watts or only 

 one-half a watt per candle power, while the 

 ordinary tungsten lamp requires about one 

 and a quarter watts per candle power. In 

 the nitrogen lamp the filament, which is of 

 tungsten, is heated to a white heat in the 

 nitrogen which fills the bulb; but the filament 

 cannot burn, for nitrogen is an inert gas, that 

 is, it will not combine with other substances. 



TUNGSTEN LAMP 

 A lamp of high candle- 



