The Spark of Genius
Thomas Edison created the first light bulb 125 years ago. But he was not only America's greatest inventor. He was also a master entrepreneur
Epiphanies. When he took the train to Ansonia with Barker and Batchelor on Sunday, September 8, it was not so much the eight big arc lamps at the foundry that excited Edison as the system he examined that morning: electric light generated not by batteries but by a primitive little dynamo, the current wired a quarter mile to the foundry. It was a double epiphany. Edison was seeing for the first time practical proof that electric power could be sent a distance--and subdivided between lamps. His next question: Could it be done at a profit? A reporter for Charles Dana's New York Sun , who had come along, captured the moment of realization: "Edison was enraptured. . . . He ran from the instrument to the lights and from the lights back to the instrument. He sprawled over a table with the simplicity of a child, and made all kinds of calculations. He estimated the power of the instrument and of the lights, the probable loss of power in transmission, the amount of coal the instrument would save in a day, a week, a month, a year, and the result of such saving on manufacturing."
Edison's intuition was to think small. Instead of sending current to create a leap of light between the electrodes of big arc lamps, useless for domestic lighting, why not send it along the wire and into a filament in a small incandescent lamp? Back at Menlo Park he worked euphorically through two nights. "I discovered the necessary secret, so simple that a bootblack might understand it," he wrote. Edison went public only a week after his visit to Ansonia. His spicy quotes got full play in the newspapers: He had not only found the way to create an incandescent bulb but would be able to light the "entire lower part of New York" with one engine and 15 or 20 dynamos: "I have it now! With a process I have just discovered, I can produce a thousand--aye, ten thousand (lamps) from one machine. Indeed, the number may be said to be infinite. . . . with the same power you can run an elevator, a sewing machine, or any other mechanical contrivance, and by means of the heat you may cook your food."
It was hot air. The "secret" was something he had visualized but not realized, a thermal regulator to cut off current to the filament before it melted or burned out. The Edison scholars Robert Friedel and Paul Israel underline his audacity: "For Edison, the search for a practical incandescent light was a bold, even foolhardy, plunge into the unknown guided at first more by overconfidence and a few half-baked ideas than by science. To suggest otherwise is to rob the inventive act of its human dimension and thus to miss an understanding of the act itself."
Other experimenters in both arc and incandescent lighting had pushed a great deal of current along a thick wire to a low-resistance filament. The real secret, Edison found, arguing it out with Charles Batchelor, was to raise the voltage to push a small amount of current through a thin wire to a high-resistance filament. It was an application of the law propounded in 1827 by the German physicist George Ohm, but it was still imperfectly understood. Edison himself said later, "At the time I experimented I did not understand Ohm's law. Moreover, I do not want to understand Ohm's law. It would stop me experimenting." This is Edison in his folksy genius mode. Understanding the relationship linking voltage, current, and resistance was crucial to the development of the incandescent lamp, and he understood it intuitively even if he did not express it in a mathematical formula.