NO. 2 HISTORY OF ELECTRIC LIGHT SCHROEDER 8/ 



and then 25 watts for iio-volt circuits were made available. Sizes 

 up to 500 watts were also made which soon began to displace the 

 enclosed carbon arc lamp. Lamps were also made for series circuits 

 in sizes from 32 to 400 candlepower. These promptly displaced the 

 carbon and Gem series lamps. The high efficiency of the tungsten 

 filament was a great stimulus to flashlights which are now sold by the 

 millions each year. The lighting of railroad cars, Pullmans and 

 coaches, with tungsten lamps obtaining their current from storage 

 batteries, soon superseded the gas light formerly used. In some cases, 

 a dynamo, run by a belt from the car axle, kept these batteries 

 charged. 



Drawn Tungsten Wire Lamp, 1911. 



Scientists had declared it impossible to change tungsten from a 

 brittle to ductile metal. This, however, was accomplished by 

 Dr. Coolidge, and drawn tungsten wire made the lamp very sturdy. 

 This lamp is in the exhibit of Edison lamps in the Smithsonian 

 Institution. 



DRAWN TUNGSTEN WIRE 



After several years of patient experiment. Dr. Williain D. Coolidge 

 in the research laboratory of a large electrical manufacturing com- 

 pany at Schenectady, N. Y., invented a process for making tungsten 

 ductile, a patent for which was obtained in December, 191 3. Tungsten 

 had heretofore been known as a very brittle metal, but by means of 

 this process it became possible to draw it into wire. This greatly sim- 

 plified the manufacture of lamps and enormously improved their 

 strength. Such lamps were commercially introduced in 1911. 



With drawn tungsten wire it was easier to coil and therefore con- 

 centrate the filament as required by focusing types of lamps. The 



