In the summer of 1878, Thomas Edison did something he hadn’t done since his honeymoon: He took a vacation. It was more of a working vacation, however. Leaving Mary behind, he joined a scientific expedition to the Rocky Mountains to see a total eclipse of the sun. With him, he brought an instrument he had invented capable of measuring minute changes in temperature. He planned to test it by measuring the heat generated by the sun’s corona - although the temperature turned out to be too hot for the device to function.

After viewing the eclipse, Edison went hunting and then traveled to California. In the two months he was gone, he and his traveling companion, George F. Barker, a professor of physics at the University of Pennsylvania, talked about the possibilities of making light from electricity. “Just at that time I wanted to take up something new,” Edison recalled.

While traveling, Edison received a letter from a friend informing him that Mary, then pregnant with their third child, was ill: “Mrs. E’s health is not the best. She is extremely nervous and frets a great deal about you and about everything. I take it to be nervous prostration.” When Mary didn’t improve, his friend telegraphed, urging him “to return at once.” Edison, who considered his wife to be something of a drama queen when it came to her health – he once drew a page of doodles turning her maiden name of Stillwell into “Stillsick” – ignored the plea and continued with his trip. He went to St. Louis to attend a meeting of the American Association for the Advancement of Science, where Professor Barker introduced him to the group as a new member. Barker praised Edison as someone who had effectively outrun the academicians: “The practical man has found science too slow and has stepped in and discovered for himself.”

Edison wasn’t the first person to generate light from electricity. As far back as 1808, Sir Humphry Davy had demonstrated so-called arc lighting to the Royal Society of London. Using a powerful battery, he sent an electric current between two carbon rods. As the current oxidized the two rods, it created a brilliant blue-white light in the shape of an arc. The implications were as dazzling as the presentation. With strong batteries and enough carbon, electric lighting could, in theory, illuminate homes and factories. But in the ensuing decades, no one had been able to overcome the technical and economic obstacles - specifically the immense size of the batteries required.

By the 1860s, arc lamps had come into limited usage in lighthouses, using electricity produced by steam-powered generators. In 1877, a Russian military engineer named Paul Yablochkov invented a regulator that allowed multiple arc lights, known as “electric candles,” to be powered by the same circuit. He demonstrated his invention by illuminating a half mile of the Avenue de l’Opéra in Paris - giving new meaning to the term City of Light.

The same year, Edison began experimenting with his own arc lights, using carbon strips as burners. But for any electric lighting to be successful on a large scale, he concluded, it would have to be part of a centralized system. For that to be possible, an enormous amount of power would have to be generated and transmitted over long distances. Each lamp would be allocated a small amount of current and would feature an affordable, high-resistance burner that didn’t generate too much heat. In the vernacular of the day, Edison would have to find a way to divide light.

Edison set out to resolve this problem in September 1878 after he returned from his trip west. That month, he visited the Connecticut brass factory of William Wallace, who, with electrical engineer Moses Farmer, had developed an electromagnetic “dynamo,” a generator powerful enough to light eight lamps at once. “Edison was enraptured,” wrote a New York Sun reporter who tagged along with him. “He fairly gloated over it . . . He ran from the instruments 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.”

Back at Menlo Park, Edison realized that Wallace and Farmer had, for the most part, solved the power generation part of the equation. The challenge that remained was “dividing” the light. Edison envisioned an electrical system similar to a municipal gas distribution system, where current would flow through main lines into smaller branches leading to homes, shops, and factories, where it could be turned on and off at will. As Edison told the Sun a few weeks after his visit to Wallace & Sons: “It was all before me . . . I saw that what had been done had never been made practically useful. The intense light had not been subdivided so that it could be brought into private houses.”

If Edison was going to divide light, he would need to package it in small, discrete units; arc lights were simply too hot and too bright to be used in confined spaces. He began experimenting with incandescent lamps, which used a metal conductor, or filament, strung between two electrodes to light up. Scientists had been trying to make incandescent lamps for decades but had been unable to get the filament to burn long enough and bright enough, and to keep the electrodes from melting.

To address the problem of oxidation, researchers in the 1830s began enclosing the metal elements of the lamp inside a glass bulb that had had the oxygen sucked out of it by a vacuum pump. In 1841, an Englishman named Frederick de Moleyns patented an incandescent light bulb that used a powdered charcoal filament heated between two platinum wires. But Moleyns’s lamp, like those that followed, was impractical and expensive, mainly because the platinum quickly disintegrated.

Just five days after he returned from Connecticut, Edison was ready to proclaim a great breakthrough. “I have struck a big bonanza,” he told the Sun. “With the 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.” Edison’s plan was to use a diaphragm to regulate the temperature and pressure inside the bulb, which he believed would prevent the filament from overheating and melting.

In this instance, Edison’s optimism may have gotten the better of him. Nevertheless, to stake his claim to the incandescent light bulb, he quickly filed a “caveat” with the U.S. Patent Office and got back to work.

From his experience working with a variety of materials in his improvements to the telegraph and telephone, Edison knew that platinum and related metals made the most sense for incandescent bulbs since they had relatively high melting points and were slow to oxidize. Platinum, however, was expensive, a major deterrent to producing a commercially viable light. Carbon, the other element scientists had used, was more easily oxidized and didn’t fare as well in a vacuum.

As Edison experimented with various materials, he took steps to line up the capital he needed to finance his large-scale electrical systems. Whatever the scientific merits of his “bonanza,” his boast had let the financial community know that America’s greatest inventor was embarking on his biggest project ever.

To pull together the venture capital, he hired a prominent New York corporate lawyer, Grosvenor P. Lowrey, to do his fundraising for him. In a letter dated October 3, 1878, Edison urged Lowrey to move quickly: “I shall agree to nothing, promise nothing and say nothing to any person, leaving the whole matter to you. All I want at present is to be provided with funds enough to push the light rapidly,” The potential investors Lowrey approached included some of the biggest names in the financial community. “You are introduced to a new class of men,” Lowrey told Edison. Investors affiliated with Edison’s longtime corporate patron, Western Union, agreed to back him, including William H. Vanderbilt, the company’s principal shareholder, who was also a major investor in gas utilities. Vanderbilt knew that if electric lighting was a success, it would make gas-fired lighting obsolete; in backing a technology that might devalue his investment, he was clearly hedging his bets.

Edison was thrilled with Vanderbilt’s support. “The electric light is going to be a great success,” he wrote in a telegraph to his European agent, Theodore Puskas, on October 5. “I have something entirely new. Wm. H. Vanderbilt and his friends have taken it in this country and on Monday next advance $50,000 to conduct experiments. I retain 1/2 the capital stock of the Co. they are to form and also receive a royalty of $30,000 yearly if it proves more economical than gas, which I am certain it will do.”

Ten days later, on October 15, the Edison Electric Light Company was incorporated in New York City. Its founders included Vanderbilt’s son-in-law, Hamilton McKay Twombly, Western Union president Norvin Green, and Egisto Fabbri, a director of Drexel Morgan Company, the leading investment bank. Banker and financier J. P. Morgan, who also sat on Western Union’s board, became personally involved in negotiating the foreign rights to Edison’s patents.

“I have been very much engaged for several days past on a matter which is likely to prove most important to us all not only as regards its importance to the world but to us in particular in a pecuniary point of view,” Morgan cabled his brother-in-law Walter Burns in Paris on October 30. “Secrecy is so essential at the moment that I dare not put in on paper. Subject is Edison’s Electric light.”

The Edison Electric Light Company was capitalized at $300,000. Of the 3,000 shares issued, Edison received 2,500 and the remaining 500 were issued to the investors. Edison got $50,000 to finance his experiments, and the company, of which he owned the lion’s share, was given the right to “own, manufacture, operate and license the use of various apparatus used in producing light, heat and power by electricity.”

The contract Edison and his backers signed was a groundbreaking step in American investment history. The investors making the deal were essentially betting on Edison’s reputation. He had not yet demonstrated that he could build a durable, economically viable light bulb, much less create the infrastructure necessary to power tens of thousands of lamps his investors envisioned illuminating the world. “Their money,” Edison commented, “was invested in confidence of my ability to bring it back.”

Now that Edison had money, he needed power - the electrical power to support his experiments at Menlo Park and test his ideas for future transmission networks. While Edison had initially been enthusiastic about the Wallace & Sons dynamo he had seen in Connecticut, he was disappointed when he hooked one of the company’s machines to his lab. The efficiency of the generator was only about 40 percent, a waste of most of the energy they needed.

To address this issue, Edison decided to invent a generator of his own. “I am all right in my lamp,” he told the Sun in mid-December 1878. “Every bit of heat is utilized to produce light as far as art will allow. The theoretical and practical results are pretty satisfactory. My point now is the generator.”

Fellow inventor Wallace took offense at Edison’s comments panning his generator; it had been built to power arc lights, not incandescent bulbs. Wallace offered to build Edison a new one, but Edison was determined to build his own. With his fresh infusion of cash, he was able to erect a new building solely for the purpose of testing large generators.

With his two principal assistants, Charles Batchelor and Francis Upton, Edison devised a dynamo that featured a pair of tall column-like electromagnets connected by a bar, which prompted his workers, all male, to dub it “long-legged Mary.” Housed in a custom-built shed behind the lab, the ungainly behemoth weighed more than half a ton. Edison’s generator, partially inspired by research done fifty years earlier by Michael Faraday, ran at an efficiency rate of 82 percent, a substantial increase over previous models. (Edison received a patent for his “dynamo-electric machine” in September 1879.)

To realize his vision for centralized power, Edison also needed to run electrical wiring underground. Unshielded wires would leak electricity and were subject to corrosion and short circuits. After experimenting with a variety of insulating materials, Edison finally decided on asphalt mixed with linseed oil, beeswax, and paraffin.

Many in the scientific community were still skeptical about Edison’s claim that electricity could be divided. An editorial in the journal Engineer declared on February 14, 1879: “If the current can be successfully divided among dozens of . . . lamps, then may gas makers quake, but nothing of the kind can be done.”

A week later, Engineer said that even if Edison could divide the current among multiple lamps, none of them would put out sufficient light: “Whether Mr. Edison’s system of utilizing electric currents for the production of light can compare favorably with other systems can only be satisfactorily demonstrated by actual experiment and experience. It will be severely handicapped by the physical drawback common to all incandescent systems, namely that for each addition to the number of lights in circuit an enormous reduction is made in the intensity of the light produced.”

In working on the electric lamp, Edison and his team had to deal with three major questions: what material to use for the filament, how to create a vacuum inside the glass enclosure, and what kind of glass could withstand the heat generated inside the bulb.

Edison began by testing a variety of materials he thought might be suitable for the filament. He needed a substance that would glow brightly and would last hundreds of hours and not crumble when the bulb was handled. Carbon had the highest known melting point, 3,500 degrees Celsius, but the carbon incandescing substance Edison was using was burning out at half that level, dissipating the light long before the temperature ceiling was reached. With platinum, he encountered the opposite problem; the filament generated light but quickly overheated. Edison tried a host of other metals, including boron, chromium, molybdenum, and osmium, but none produced the long-lasting light he was looking for.

Edison also experimented with non-metallic substances, sending to South America and the East Indies for exotic plants. “Before I got through,” he wrote, “I tested no fewer than 6,000 vegetable growths and ransacked the world for the most suitable filament material.” None solved his problem. In his attempts to keep the metal from melting, he produced a blinking light, not at all what he was aiming for.

In the meantime, Edison searched for ways to create a near-perfect vacuum in a glass globe. His glass blower, a German émigré named Ludwig Boehm, achieved that with a pump invented by countryman Hermann Sprengel, which used drops of mercury to compress the air before it was evacuated. With a more complete vacuum, Edison was able to construct a more durable platinum-based lamp. On April 12, 1879, he applied for a patent for his high-resistance platinum-enhanced vacuum light. Still, Edison was dissatisfied. Platinum was expensive and in short supply, making it a highly impractical solution.

Edison’s backers on Wall Street, initially impressed by his promise to create cheap, abundant electric light, were not pleased with Edison’s progress. In their eyes, the money he was spending did not justify the paltry results they were seeing. To reassure them, Edison’s lawyer, Grosvenor Lowrey, suggested inviting the Wall Street men to Menlo Park so they could see for themselves what Edison had done. Edison resisted, but finally agreed. On a dark, rainy day in April, several of his financiers, including J. P. Morgan, took the train to Menlo Park, where Edison and his assistants had set up platinum lamps for display. The investors were not encouraged; the prototypes glowed only briefly, and the light they emitted was dim. One backer had the temerity to suggest to Edison that he had taken the wrong tack by using a high-resistance filament rather than the low-resistance type that other experimenters were trying.

As word of the disappointing demonstration got out, Edison’s efforts were now seen as dubious, even ridiculous. William Preece, the chief engineer of the British Post Office, pronounced in a lecture that “a subdivision of light is an absolute ignis fatuus” - a witty play on a Latin phrase that translated figuratively to a “deceptive goal or hope.” In the United States, rival inventor William Sawyer declared Edison’s latest lamp patent “nothing new” and said his research was bound to end in “final, necessary, and ignominious failure.”

After the financiers’ visit, Edison put the platinum-filament lamps aside and searched for alternate solutions. “The electric light has caused me the greatest amount of study and has required the most elaborate experiments,” Edison remembered. “I was never myself discouraged, or inclined to be hopeless of success. I cannot say the same for all my associates.”

A year after he began his search, Edison turned again to carbon. It had a high melting point and high electrical resistance; plus it was cheap and easy to find. In his book, Menlo Park Reminiscences, Francis Jehl, one of Edison’s lab assistants, recalled how Edison came up with the right iteration of carbon for his lamps: “Sitting one night in his laboratory reflecting on some of the unfinished details, Edison began abstractedly rolling between his fingers a piece of compressed lamp black mixed with tar for use in his telephone. For several minutes his thoughts continued far away, his fingers meanwhile mechanically rolling the little piece of tarred lampblack until it had become a slender filament. . . . He conceived the idea that it might give good results as a burner if made incandescent.”

In a series of experiments undertaken in a shed behind the Menlo Park lab, workers burned smoky kerosene lamps and collected the resulting black smudge from the glass, forming it into carbon cakes. The cakes were then mixed with tar and kneaded into reeds with a diameter of one sixty-fourth of an inch. From these reeds, the workers were able to form threads as thin as seven one-thousandths of an inch.

In the fall of 1879, Edison began his round-the-clock quest for the perfect incandescent electric light. He slept no more than four hours a day and expected his workers to do the same. Edison “could never understand the limitations of the strength of other men because he own mental and physical endurance seemed to be without limit,” recalled Francis Upton.

As Edison and his workers searched for the perfect carbonized filament, they tried all kinds of raw materials, including flax, silk, hemp, fishing line, teak, spruce, boxwood, and vulcanized rubber. “The most interesting material of all that we used in our researches after a successful filament was the hair from the luxurious beards of some of the men about the laboratory,” wrote Jehl. The human hair, Jehl reported, “burned out with considerable rapidity.”

In October, Edison tried a variation on the carbon thread approach. Taking a length of ordinary cotton thread, he stretched it between two iron clamps and put it in the furnace, causing it to carbonize. For days, he and his assistants worked to come up with carbonized threads that would not break when strung between the lamp’s platinum lead-in wires. The night of October 21, they tested nine variations of carbonized filaments inside a vacuum bulb. The laboratory notebooks from that night and the next day record the results for the ninth type of thread: “No. 9 on from 1:30 a.m. till 3 p.m. - 13 1/2 hours and was then raised to 3 gas jets for one hour then cracked glass and busted.”

That matter-of-fact notation marks the birth of Edison’s incandescent light. “If it can burn that number of hours, I know I can make it burn a hundred,” Edison told his elated workers. The next No. 9 filament they tested lasted more than forty hours.

Forty years later, Edison still remembered the occasion: “The lamp was hermetically sealed and then taken off the vacuum pump and put on the electric current, it lighted up. . . . Then we sat down and looked at that lamp. We wanted to see how long it would burn. . . . None of us could go to bed, and there was no sleep for any of us for forty hours. We sat and just watched it with anxiety growing into elation. The lamp lasted about forty-five hours and I realized that the practical incandescent lamp had been born.”

The patent application Edison filed on November 1, 1879, reads in part: “I have discovered that even a cotton thread, properly carbonized and placed in sealed glass bulbs, exhausted to one millionth of an atmosphere, offers from one hundred to five hundred ohms’ resistance to the passage of the current and that it is absolutely stable at a very high temperature.”

Edison concluded his patent application by asserting: “I claim as my invention an electric lamp for giving light by incandescence, consisting of a filament of carbon of high resistance, made as described, and secured to metallic wires.”

In the nearly three months it took for the patent to be granted on January 27, 1880, Edison worked furiously to improve his carbon filaments. Since cotton was made from a plant, he and his team tried other natural materials, including baywood, boxwood, cedar shavings, flax, coconut shells, and plumbago. In the end, they found that threads extracted from cardboard and then carbonized lasted the longest, 170 hours.

Edison, who had never been shy about publicizing his electric-light “breakthroughs,” held his tongue until he was confident he had found the best filament possible. But he was again out of money. In November, two of J. P. Morgan’s partners, Egisto Fabbri and J. Hood Wright, came to Menlo Park to see what he was up to. By this time, Edison had rigged up his own home and the residence of one of his top deputies, Francis Upton, with electric lights.

The inventor told his visitors he had spent all the money the investors had given, plus some of his own. He begged them for funds to build a pilot power station at Menlo Park.

Morgan’s men, while impressed by the light bulb, weren’t convinced that Edison was on the verge of creating an entirely new industry. Grosvenor Lowrey, now Edison’s most ardent supporter as well as his lawyer, tried to persuade them to see the bigger picture. In a letter he wrote to Edison on November 13, 1879, he reported what he had said to the board: “It was not to be forgotten that you were presenting to them the greatest return for capital that was ever offered and giving, hourly, the resources of your talent, and knowledge, & devoting your health too, which only one man in the world possessed.” Lowrey reminded board members that “plenty of people had capital,” but they were the only ones who had Thomas Edison. Despite his heartfelt appeal, Lowrey succeeded in securing only $5,000 in additional funding for Edison.

Realizing that this wasn’t enough, Lowrey decided to start the publicity mill grinding. Edison had already agreed to talk with Marshall Fox of the influential New York Herald on the condition that the reporter hold his story until Edison was ready to go public. Now it was time to give Fox the green light.

The Herald’s front page article was published on December 21, 1879, with a litany of subheads that left no doubt as to the historic significance of Edison’s invention:

EDISON’s LIGHT

The Great Inventor’s Triumph in Electrical Illumination.

A SCRAP OF PAPER

It Makes a Light, Without Gas or Flame, Cheaper Than Oil

TRANSFORMED IN THE FURNACE

Complete Details of the Perfected Carbon Lamp.

FIFTEEN MONTHS OF TOIL

Story of His Tireless Experiments with Lamps, Burners and Generators.

SUCCESS IN A COTTON THREAD

But the word was out, and the public demanded a demonstration of Edison’s epic new invention, whether or not Edison was ready to give them one. In the final days of 1879, thousands of spectators traveled to snow-covered Menlo Park to gawk at the lamps - and at their creator. Special trains were added to bring in the sightseers. What they saw was a generator powering a few dozen lights. It was only a glimpse into an electric future, but the crowd was thrilled nonetheless.

On New Year’s Eve, 3,000 people traipsed through Edison’s lab and the generator shed, some dressed in formal attire more suited to a Manhattan soiree than a scientific demonstration in rural New Jersey. This time, Edison put on quite a show, as the Herald reported: “The laboratory was brilliantly illuminated with twenty-five electric lamps, the office and counting room with eight, and twenty others were distributed in the street leading to the depot and some adjoining houses. The entire system was explained in detail by Edison and his assistants, and the light subjected to a variety of tests . . . Many had come in the expectation of seeing a dignified, elegantly dressed person, and were much surprised to find a simple young man attired in the homeliest manner, using for his explanations not high sounding technical terms, but the plainest and simplest language.”

Despite Fabbri’s misgivings, the demonstration was a resounding success. Early in 1880, the investors put up another $57,568 to underwrite Edison’s plan to build a preliminary power station and network, complete with insulated copper wires installed underground. If all went well, that system would be a precursor to a much larger undertaking: the electrification of ten city blocks in lower Manhattan.

In April, Edison latched onto a new opportunity to show off his lighting system. One of his investors, Henry Villard, president of the Oregon Railway and Navigation Company, was building a steamship - the Columbia - in New York and asked Edison if he would install an electric lighting system on board. Edison outfitted the ship with four dynamos and wired 115 lamps. The ship sailed around Cape Horn to California, a voyage of two months. Despite prophecies, no fire broke out at sea, and the ship arrived in San Francisco with all its lamps still aglow after 415 hours of use.