Edison and the Electric Chair_ A Story of Light and Death - Mark Essig [12]
Edison believed he could domesticate electric light. As he explained it, electric light "had never been made practically useful. The intense light had not been subdivided so that it could be brought into private houses."5
The principle behind Edison's "subdivided" light was known as incandescence—using electricity to heat a material until it glowed. The flow of electric current along a conductor depends on the relationship of voltage, resistance, and amperage. Voltage is the electrical pressure that causes current to flow. Resistance (measured in units called ohms) is the opposition that a conductor offers to current; when current encounters resistance, some of the electrical energy is converted into heat. Amperage is the rate of flow of electricity along the conductor, established as voltage overcomes resistance. Whereas the arc lamp relied on brute force—high-pressure electricity (500 to 1,000 volts) hurtling down a copper wire and leaping a gap between carbon rods incandescence required a delicate touch. In the system Edison envisioned, a low pressure of 100 volts or so flowed smoothly from the generator through low-resistance copper conducting wires until it encountered the burner, which had a higher resistance and therefore impeded the flow, causing some of the electricity to be transformed into heat; the heat raised the temperature of the burner to incandescence, producing light.
The theory was simple, the practice excruciatingly difficult. When heated to temperatures high enough to incandesce, most materials either oxidized (burned) or fused (melted). The two most promising candidates were carbon, which had an extremely high melting point but tended to burn; and platinum, which did not burn but tended to melt. Inventors—including the Englishman Frederick De Moleyns and the Americans J. W. Starr and Moses Farmer—had experimented with these two substances as far back as the 1840s, but no one had created an incandescent lamp that glowed for more than a few seconds before disintegrating.6
AS SOON AS Edison returned from his visit to Wallace on September 8, he sketched a plan for a light in his laboratory notebook. Two days later he conducted his first experiments, and three days after that he wired to Wallace to inquire about the generator he had ordered: "Hurry up the machine. I have struck a big bonanza." Edison's laboratory notebooks reveal the nature of his alleged success. The inventor decided that carbon's tendency to burn rendered it useless, so he discarded it in favor of platinum. To skirt the problem of platinum's melting, he devised a thermal regulator: When the temperature of the platinum approached the melting point, a piece of metal would expand and break the current; when the regulator cooled, the current flowed again.7
"I have it now!" Edison proclaimed in the pages of the New York Sun on September 16. "When the brilliancy and cheapness of the lights are made known to the public," he said, "illumination by carburated hydrogen gas will be discarded."8
Upon the announcement of Edison's invention, stocks of illuminating gas companies plunged on the New York and London exchanges and investors scrambled to buy a stake in the new light. The Edison Electric Light Company was incorporated and capitalized at $300,000, with Edison receiving $50,000 to develop his invention. Investors included William H. Vanderbilt, the principal shareholder in Western Union;