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OUR PHYSICAL WORLD 



the air would promptly combine with oxygen or burn, it was 

 necessary to exhaust the air from the electric-light bulb or to 

 fill the bulb with some gas like nitrogen or argon that does 

 not unite with carbon. 



It was an American, W. Starr, who in 1844 invented the first 

 incandescent lamp. A thin strip of carbon in a glass capsule 



from which the air had been exhausted 

 produced a light as the carbon glowed 

 with the current sent through it. The 

 next year a Frenchman, De Changy, 

 used lamps with filaments of platinum 

 for lighting the workings in coal mines. 

 Progress was gradually made, but the 

 incandescent lamp remained a crude 

 affair until Edison worked on it in 1878, 

 when he made so many improvements 

 that he is looked upon as its real in- 

 ventor. He used a carbonized fiber of 

 bamboo which was attached to plati- 

 num wires so fused into the glass of 

 the bulb that the latter could be made 

 sufficiently air-tight to hold the vacuum 

 for a long time. Recently, in place of 

 the carbon, filaments of metals like 

 tantalium or tungsten are used. Rare 

 ores are made to yield these metals, and 

 the invention of methods for making 

 them malleable and ductile was very 

 difficult. This task was necessary, 

 however, as naturally these metals are very brittle and fragile. 

 But now a single pound of tungsten makes 30 miles of fila- 

 ment that stands a temperature of 5,000 F. A carbon 

 filament could not stand even half the temperature neces- 

 sary to produce the more intense incandescence of the wire 

 (Fig. 108). 



FIG. 108. Diagram of an 

 electric light. 



