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
Scientists in America and England who were still thinking of low resistance and thicker and thicker wires (at great cost) dismissed Edison's project to light New York as both scientifically stupid and economically hopeless. But he had to find a filament of high resistance--and heat it up to incandescence in a bulb as close to airless as he could get to hinder oxidization. Edison was not even close to resolving these dilemmas in the early fall of 1878 when his friend and lawyer Grosvenor Lowrey (who had encouraged Edison to fly his colorful kite in the press) moved on his behalf in New York's banking parlors. Lowrey swiftly raised $300,000 to form the Edison Electric Light Co. The filament proved more elusive than Edison had hoped. He had discarded carbon because it burned up so readily. Platinum wire offered only low resistance but did not oxidize and therefore seemed to offer the best prospect. They worked on making long spirals of thin platinum, to increase the resistance, but it was delicate and dangerous work. In mid-April, Lowrey led a group of investors into the darkened lab where Edison had installed 12 lamps with a platinum filament linked in series. Edison told John Kruesi to turn on the current slowly. Francis Jehl, an assistant, recalls: "I can see those lamps rising to a cherry red and hear Mr. Edison saying, 'A little more juice,' and the lamps began to glow. A little more . . . and then one emits a light like a star after which there is an eruption and a puff, and the machine shop is in total darkness." Batchelor replaced the dud lamp; the same thing happened a few minutes later. Only Lowrey's eloquence and the steadfastness of 42-year-old John Pierpont Morgan held the group together.
The other challenge was the vacuum; nobody had been able to get enough air out of the bulb. Edison did a simple thing. He had put a classified advertisement in the New York Herald for a glass blower, which netted an 18-year-old in a little red German student cap. The mechanics were amused by the dainty Ludwig Boehm and his pince-nez, but he blew a better bulb to Edison's design and he helped work out a new way of evacuating a bulb by infusions of mercury. It was laborious, frustrating work, but in September, after weeks of effort, Edison and his team achieved a vacuum of one hundredth of an atmosphere. Edison discovered that at this level they had so reduced the oxygen in the bulb that a carbon stick did not burn up quickly and it gave a better light than platinum ever had. That was the good news; the less good was that resistance to this particular piece of carbon was only around 2 ohms (which would mean more current, more copper). Resistance could be raised by shaping a tiny filament in a small spiral, but the filament would have to be no thicker than 15 thousandths of an inch. Edison set everyone in a frenzy trying to roll carbon into reeds no thicker than thread. Day after day, night after night, the spiral reeds kept breaking.