History : Jul-Aug 2016
NATIONAL GEOGRAPHIC HISTORY 81 Edison assumed that he could pass a current through a platinum filament, and the heat would cause the filament to incandesce. However, he discovered that oxygen attacked and weakened the platinum when it was heated. To overcome this problem, Edison placed the metal filament in a vacuum bulb. While the vacuum improved the performance of his lamps, platinum was still too costly and also had a low electrical resistance, which meant his future system would need large and expen- sive copper cables. Fortunately, Edison realized that he could overcome the need for large cop- per distribution mains by increasing the resistance of each lamp and putting them in parallel circuits. The challenge now became find- ing a high-resistance filament. For sev- eral months in 1879, Edison and his team tried dozens of materials, only to find that the lampblack carbon Edison had been using in his telephone transmitters was the ideal material. As one newspaper report described the Eureka moment: Sitting one night in his laboratory reflecting on some of the unfinished details, Edison be- gan abstractedly rolling between his fingers a piece of compressed lampblack until it had become a slender thread. Happening to glance at it, the idea occurred to him that it might give good results as a burner if made incandes- cent. A few minutes later the experiment was tried, and to the inventor’s gratification, satis- factory, although not surprising results were obtained. Further experiments were made, with altered forms and composition of the substance, each experiment demonstrating that the inventor was upon the right track. In October 1879 Edison and his staff conduct- ed their first successful experiments by putting a carbon filament in a vacuum, and they were able to bring it to incandescence since there was no oxygen to cause the filament to burn. By New Year’s Eve, Edison was demonstrating lamps using carbonized cardboard filaments to large crowds at his Menlo Park laboratory. MPI/GETTY IMAGES LEBRECHT MUSIC/ALBUM SUPER SOUNDS OF THE (EIGHTEEN) SEVENTIES One of his most successful creations, Edison’s phonograph was invented in 1877. Production of this model began in 1898 and lasted for 15 years. I’LL TAKE NEW YORK. IN THIS CURRIER & IVES PRINT FROM THE LATE 1800s, EDISON (LEFT) AND CHARLES BRUSH, INVENTOR OF THE ARC LAMP, ARE SHOWN AS RIVALS OVER LIGHTING UP NEW YORK.