ON AUGUST 26, 1878, Edison arrived back in Menlo Park and was reunited with his wife, Mary, and his daughter and son, five-year-old Marion and two-year-old Tom Jr.—nicknamed Dot and Dash by their father, ever the telegraph man. When reporters appeared to collect news of the trip, the inventor spoke rapturously about the West, complaining only about the springless stagecoaches at Yosemite: "If they had only fastened a good stout plank on the seat of a fellow's trousers, and employed an able-bodied mule to kick him uphill and over the canyons, it would have been a big improvement." The day after his return, Edison headed to his laboratory and started research on the electric light.1

The source of excitement among the scientists on the western trip was a new version of the electric arc lamp that had just been unveiled at the Paris Universal Exposition by the Russian engineer Paul Jablochkoff. The light's basic principle—running a strong electric current across a gap between two slender carbon rods—had been discovered by Humphry Davy seventy years before, but the technology had changed dramatically over the decades. Whereas Davy had used electricity created by a chemical battery, the Jablochkoff lamps used the latest design of electrical generator.

Because the understanding of electricity as a movement of electrons in a conductor would not emerge until around 1900, in the 1870s not even the greatest electricians could claim to know just what happened inside a copper electric wire. But this lack of theoretical understanding did not prevent scientists from becoming adept at manipulating electrical force. Faraday had discovered that moving a coil of conducting wire through the lines of force of a magnetic field caused current to flow in the conductor, and later experimenters learned that they could increase the strength of the current by using stronger magnets and multiplying the number of coils of conducting wire. The first generators employed permanent steel magnets, which were relatively weak. To skirt this difficulty, inventors in the late 1860s turned to the discovery that first inspired Faraday—the ability of electric current to produce a magnetic field—and built generators that replaced permanent magnets with far more potent electromagnets. At first the current for the electromagnets was supplied by batteries or smaller generators, but in the 1860s and 1870s inventors designed generators that produced the current for their own electromagnets. Because these machines excited their own magnetic fields, they were known as dynamo-electric generators, or dynamos. The new machines could produce a current that was powerful, steady, and inexpensive enough for arc lighting.2

In the Jablochkoff arc lamp system, the creation of light started with the burning of coal, which heated water in a boiler and produced steam. The steam drove the piston in an engine, and the piston moved a driveshaft, which was connected via a leather belt to the dynamo. The belt turned the dynamo's armature, an iron core wrapped with coils of copper wire. As it spun at hundreds of revolutions per minute, the armature repeatedly cut through the lines of force of an electromagnet. The movement of a conductor (the armature) through the magnetic field produced an electric current, which flowed through copper wire to the lamps, each of which contained two pencil-thin rods of carbon a fraction of an inch apart. The current leaped the gap between the carbon rods—producing a powerful light—then flowed on to the next lamp. The process moved from coal to steam to mechanical motion to electricity; it was a simple matter of the transformation of energy, from black coal to white light.

On September 8, 1878, two weeks after returning from his western trip, Edison visited the Connecticut factory of William Wallace, who in the previous few months had developed his own system of arc lighting. A newspaper reporter described the inventor's reaction to Wallace's factory: "Mr. Edison was enraptured. He fairly gloated over it. . . . He ran from the instruments to the lights, and from the lights back to the instruments. He sprawled over a table with the SIMPLICITY OF A CHILD, and made all kinds of calculations." Edison ordered a generator from Wallace, then returned to Menlo Park.3

When he began his lighting experiments, Edison chose not to focus on the arc lamp, because he noticed its limitations: It produced an intense glare and—because the carbon rods combusted—emitted choking fumes, making it suitable for use only outdoors or high overhead in factories. The arc lamp's blaze was measured in the thousands of candlepower, whereas home lighting required only a dozen or so. In most larger cities, homes and offices were lit with illuminating gas, which gave a soft, gentle light but also flickered and released gases (ammonia, sulfur, carbon dioxide) that poisoned the air, and soot that blackened the walls. Worse, the open flames of gaslight set buildings on fire with alarming regularity.4

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; Norvin Green, the president of Western Union; and Egisto Fabbri, a partner at Drexel, Morgan & Company, the nation's leading investment banking firm. J. P. Morgan himself, normally a cautious investor who avoided risky new ventures, had no doubts about Edison—at his direction Drexel, Morgan snapped up British rights to Edison's light patents and became his agents for all of Europe.9

New York's financiers poured money into the creation of the Edison Electric Light Company because they were terrified of being left behind. Vanderbilt and other Western Union stockholders had seen firsthand how Edison's quadruplex and other inventions reshaped the telegraph industry, and they expected that he would do the same to the world of lighting. The investors expected nothing less than a technological and social revolution, a new service that no home or office could do without. The potential profits were immeasurable.

There was only one problem with Edison's announcement and the frenzy it produced: Fie had not, in fact, invented a working incandescent light.

Edison certainly thought he was closer to success than he was, but there may have been another motive behind his premature announcement. To invent the lightbulb, Edison needed a great deal of money, far more than investors would give him for early-stage experiments. So he simply said he had already finished. By making the premature announcement in the Sun, he hoped to fire public enthusiasm and pry open the coffers of Wall Street. The ploy worked. With the investors' money in hand, Edison set to work on the invention he claimed to have already perfected.10

"I WAS ALWAYS AFRAID of things that worked the first time," Edison had said two years earlier, after his surprisingly quick success with the phonograph. He had nothing to fear from the electric light. As work proceeded in the fall of 1878, the thermal regulator remained balky and the platinum burners still melted. Edison began to understand that the task was much larger than he had imagined.11

Fortunately, he was well prepared. Edison's successes depended in part upon the work environment he created at Menlo Park. The location in rural New Jersey offered seclusion from but also proximity to the centers of capital in New York. Although he complained about the "damned capitalists," it was their money that built him the best laboratory in the world—complete with a new machine shop, a stockroom filled with every metal and chemical known to science, and an enormous library of scientific journals and books.12

The money also allowed Edison to hire assistants of extraordinary talent. Foremost among the Menlo Park staff was Charles Batchelor, an Englishman with a bushy black beard and considerable skill as a machinist and draftsman. Batchelor had started working for Edison in Newark in 1871 and immediately emerged as the inventor's chief assistant, his methodical work habits complementing Edison's cut-and-try enthusiasm. Another top associate, John Kruesi, trained as a clockmaker in the legendary shops of Switzerland before joining Edison's team, and those skills served him well when he was called upon to translate Edison's crude sketches into working models. Kruesi built the first phonograph in just six days, and it worked the first time it was tried. The newest arrival, Francis Upton, was a Princeton-trained mathematical physicist who had studied in Berlin with Hermann von Helmholtz; Upton joined the staff in 1878 to help with the lighting experiments. A touch insecure about his own lack of formal training in mathematics, Edison liked to tease Upton about his fancy degrees. But he was venturing into territory where mathematical ability was essential, and part of his brilliance was in recognizing that Upton's mathematical talents balanced his own more intuitive grasp of technology. 13

Newspapers reported that in the early evening, when most workers could expect to go home to their families, Edison's men were just hitting their stride. After assembling to review accomplishments and chart strategy, they dispersed to their individual tasks. Edison hustled from bench to bench, observing experiments and giving instructions. Then he would stop and become absorbed in a particular experiment. His thin hands floated above an instrument, darting in to make minute adjustments, while the rest of his body stood as rigid as stone.14

A little before twelve o'clock on many nights, two apprentices and a huge Newfoundland dog would set out for the local grocery. Menlo Park had no streetlights, electrical or otherwise, so the dog led the way with a lantern clamped in his teeth. After rousing the grocery keeper from bed, the party returned with baskets laden with soda crackers, cheese, butter, and ham. A boy fetched buckets of beer from Davis's Lighthouse, the local tavern, and the Menlo Park crew gathered for their midnight supper. After the meal Edison passed out cigars, and amid the smoke the men gossiped and told jokes. Some nights there was clog dancing, or an impromptu boxing match, or a sing-along to popular tunes. The German glassblower Ludwig Boehm might play the zither and yodel. Often "the old man"—as the workers called Edison—would sit down at the pump organ and pound out the few chords he knew. Then the boss would stand and hitch up his trousers—the signal to get back to work. Visiting reporters often got so caught up in the fun that they missed the last train back to New York and spent what was left of the night sleeping on the laboratory floor.15

Their host often chose similar accommodations, even though his wife and a warm bed awaited him just a short walk away. One of Edison's favorite locations was a small storage closet under the laboratory's stairwell. He would crawl in, pull the door shut, and sleep for a few hours on the floor. (This space doubled as his hiding spot when unwanted visitors arrived.) He also liked to stretch out under one of the lab benches, using his coat as a pillow—but not before giving his men orders to wake him if anything important developed. According to one reporter, "Life in the Menlo Park laboratory partakes more of the character of a camp pitched near the battlefield than of anything else."16


Edison (seated in the middle with a scarf around his neck) with some of his assistants at the Menlo Park laboratory, February 1880.

EVEN AFTER FOUR MONTHS of unsuccessful experiments, Edison remained convinced that platinum was the best material for an incandescent burner. Previously, he had tested his platinum burners in the open air, but when he still could not keep them from melting, he decided to try a new technique. In late January 1879 he started placing the burner within a glass container evacuated of air—for the first time, he was working on a light bulb. Earlier inventors had tried coupling a vacuum with carbon burners in an attempt to avoid oxidation, but they had trouble creating a good vacuum. Edison at first believed that his decision to focus on platinum, which did not burn, had freed him from the need for a vacuum, but by late January he began to think otherwise. He discovered that bubbles of gas were being trapped within the platinum burners, causing them to melt more easily. If he heated platinum in a vacuum, Edison reasoned, he would release the occluded gases and raise the melting point of the platinum. The available vacuum pumps—complex contraptions of glass tubing and liquid mercury—did not work well enough, so Edison devised a new one that evacuated nearly all of the air from a glass globe.17

The vacuum pump was not the only new device at Menlo Park. Although initially impressed by William Wallace's electrical generator, Edison discovered that it, like all of the other generators on the market, could not produce a current efficient enough for economical incandescent lighting. Edison and his men began to experiment on designs of their own. By the spring of 1879 they had created what Upton called "the best generator of electricity ever made," one that converted mechanical energy to electrical with very little waste. The Edison dynamo featured two large, cylindrical magnets standing on end, an arrangement that, to the fertile imaginations of the men at Menlo Park, resembled a woman on her back with her legs in the air. They duly nicknamed the new machine the "long-legged Mary-Ann," although prudish newspaper editors confusingly revised that to "long-waisted."18

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 carbon, was used in the carbon buttons for the transmitter, and there was always a great deal of the material around the laboratory. A newspaper account described the eureka moment: "Sitting one night in his laboratory reflecting on some of the unfinished details, Edison began abstractedly rolling between his fingers a piece of compressed lampblack mixed with tar for use in his telephone . . . until it had become a slender filament. Happening to glance at it the idea occurred to him that it might give good result [sic] as a burner if made incandescent."25

When he first started work on the lamp, Edison abandoned carbon because of its tendency to burn, and because all earlier inventors had used thick carbon rods of low resistance. In the fall of 1879, however, he realized that he could make carbon just as thin as platinum wire. With his new, powerful vacuum, the carbon would not burn—no oxygen, no oxidation. After experimenting with different types of carbon burners, Edison and Batchelor took a piece of cotton thread, .0013 of an inch in diameter, and carbonized it in an oven. The filament—as the slender burners were now called—was attached to platinum lead-in wires and sealed inside an evacuated glass bulb. The lab notebook entry tells the tale: "on from 1:30 AM till 3 pm[:] 13 1/2 hours and was then raised to 3 gas jets for one hour then cracked glass & busted." It was an understated entry for a historic event. Edison and his men had finally created a practical incandescent lamp—one that would burn for hours and use very little energy.26

"It is an immense success," Edison told a friend. "Say nothing." Although it went against his nature, he remained silent because he wanted to be absolutely sure of success before the press learned of it. Dissatisfied with the carbon thread, Edison and his men tested hundreds of different sources of carbon. Finally, at Bachelor's urging, they tried a horseshoe-shaped piece of cardboard boiled in sugar and alcohol and then carbonized. It worked even better than carbon thread. "I think the Almighty made carbon especially for the electric light," Edison told a reporter.

Now Edison was ready to exhibit his light.27

He invited the public to Menlo Park for New Year's Eve, 1879, and before nightfall the roads to the town were clogged with carriages, wagons, and pedestrians, and railroad companies ordered special trains to carry the crush. Thousands of spectators thronged the streets until past midnight. When Edison appeared, attired in a rough suit of work clothes, the crowd surged toward him. Some shouted questions, ranging from "How'd you get the red-hot hairpin into that bottle?" to more informed queries about the horsepower required to power each bulb. Edison had become an expert at working a crowd, playing the role of the modest genius, explaining complex science in simple terms.28


The Edison incandescent lamp as it appeared in 1880.

The system was powered by three long-legged Mary-Ann dynamos and controlled by a telegraph key in the machine shop. The visitors never tired of pressing the key, turning the lights off and on. When one of Edison's men plunged a lamp into a jar of water, the crowd was astonished to see that the water did not quench the flame. But the lights in open air were astonishing enough. Two lamps glowed softly at the entrance to the library, eight more atop wooden poles along the roadway, and a string of thirty lit up the laboratory building.

To modern eyes, it would have seemed a rather modest display. But those assembled were among the first people in the world to see the marvelous glow of incandescent light. No flame, no flicker, no soot, no fumes—just pure, steady light.29

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