THE BANISHMENT OF NIGHT 



ceased his efforts until a practical incandescent lamp 

 had been produced. His idea was to perfect a lamp 

 that would do everything that gas could do, and more; 

 a lamp that would give a clear, steady light, without 

 odor, or excessive heat such as was given by the arc 

 lights in short, a household lamp. 



Early in his experiments he abandoned the voltaic 

 arc, deciding that a successful lamp must be one in 

 which incandescence is produced by a strong current 

 in a conductor, the heat caused by the resistance to the 

 current producing the glow and light. But when search 

 was made for a suitable substance possessing the neces- 

 sary properties to be the incandescent material, the in- 

 ventor was confronted by a vast array of difficulties. 

 It was of course essential that the substance must re- 

 main incandescent without burning, and at the same 

 time offer a resistance to the passage of the current 

 precisely such as would bring about the heating that 

 produced incandescence. It should be infusible even 

 under this high degree of heat, or otherwise it would 

 soon disappear; and it must not be readily oxidizable, 

 or it would be destroyed as by ordinary combustion. 

 It should also be of material reducible to a filament 

 as fine as hair, but capable of preserving a rigid form. 

 These, among others, were the qualities to be con- 

 sidered in selecting this apparently simple filament for 

 the incandescent lamp. It was not a task for the tyro, 

 therefore, that Edison undertook when he began his 

 experiments for producing an "ideal lamp." 



The substance in nature that seemed to possess most 

 of the necessary qualities just enumerated was the metal 



[229] 



