Edison and the Electric Chair_ A Story of Light and Death - Mark Essig [15]
With the new vacuum pump and the new dynamo design, Edison believed he stood on the eve of triumph, so in March of 1879 he once again called in the newspaper reporters. A few minor problems remained to be cleared up, Edison said, but even now his light could be "put in practical operation everywhere, and electricity supplied at less than half the cost of gas."19
The announcement, as before, turned out to be premature—the platinum burners still did not work properly. When it became clear Edison again could not make good on his claims of success, his investors became nervous, gas stocks rebounded, and critics sharpened their knives. "Day after day, week after week and month after month passes and Mr. Edison does not illumine Menlo Park with his electric light," the normally loyal Daily Graphic observed. "The belief has become rather general in this country and in England that for once the great inventor has miscalculated his inventive resources and has utterly failed."20
The "long-legged Mary-Ann" dynamo.
Franklin Pope, Edison's erstwhile friend and mentor, wrote a bitter anonymous letter to the Telegraphic Journal: "I know of no one here (whose opinion is worth anything) who has any confidence in the practical success of Edison's scheme. The way that the world stands agape waiting for the Edisonian mountain to bright forth its mouse is really absurd."21
As criticism mounted, Edison remained calm. "It has been just so in all of my inventions," he explained to a friend. "The first step is an intuition and comes with a burst—Then difficulties arise. This thing gives out then that. 'Bugs' as such little faults and difficulties are called, show themselves—Months of intense watching, study and labor are required before commercial success—or failure—is certainly reached." He neglected to mention that, back in September, he had already guaranteed commercial success.22
Although Edison's chosen material—platinum—still refused to work, Edison did hit upon a key insight into the theory of burners. All previous inventors who worked on the incandescent lamp employed a burner of fairly low resistance, one ohm or so, because they assumed that raising the resistance of the burner would require the use of more energy, thus boosting costs. Edison was the first to understand that energy consumption was proportional to the burner's radiating surface, not to its resistance. As Edison explained to a newspaper reporter, "The point is that the more resistance your lamp offers to the passage of the current, the more light you can obtain with a given current." Edison set out to create a burner with 100 times or more the resistance of those used by earlier inventors.23
Putting the theory of high resistance into practice proved more difficult. The resistance of a conductor was inversely proportional to its diameter—the thinner the wire, the higher the resistance. An appropriate platinum burner would have to be long and slender, and a long piece of wire would fit within a small glass globe only if it were wound into a tight spiral. This required the wire to be insulated, so that the turns of the spiral could touch each other without shorting out. Edison and his crew tried dozens of insulating substances—including barium nitrate, sodium tungstate, calcium acetate, and silk coated with magnesia—but none worked.24
The breakthrough finally came in October of 1879—a year after he first announced success—and, as with the phonograph, it resulted from his practice of working on several different projects at once. When Edison's carbon telephone transmitters entered the market, a crew was assigned to produce them. In a small shed beside the laboratory, kerosene lamps burned constantly, and workmen periodically scraped off the soot that collected on the lamp chimneys. The lamp36 black, a high-grade