PI: At the time that Edison began working on the incandescent light, there were commercial arc lights. These are very powerful lights where a gap between two carbon poles allowed a spark to pass and this created a huge light, that was great for outdoors, but … not very good for interior lighting. And so what Edison wanted was a much softer light and the way you did this was to heat something up so that it incandesced, that is, it glowed, kind of a white or yellowish-white light, as the lamps that we have today. And that's what he was looking for, something that would be a much softer light that could be sort of divided amongst the rooms, instead of having one large powerful light.
PI: Well, what he was looking for was what would be an appropriate burner. For the first few months, what he chose was platinum. You take a platinum wire, very thin, coil it up. As it heats, it goes from a red to a kind of yellowish, to finally a bright white glow. In fact, about the same candle power as a gas light, but a purer light than you would get with gas, where you have various kinds of things in the chemicals of the gas that made it not quite as good a light. And, in fact, one of the first facilities that used his lamp was a printing press, and they found it just gave a better light for looking at the colors of their operations and so forth. And so that's what he was looking for, was something that he could heat up to incandescence and eventually he would turn to carbon, after about a year of research.
PI: After working for a while on his lamp, Edison decided that he needed to investigate better the materials he was using. He was heating up these platinum filaments in the air and they would last for a very short period of time and he was trying to get them to last much longer. So he began to look at them under the microscope, studying them under different conditions of heating and he began to discover cracks and air bubbles in them, and so he thought to himself, well, I need to protect this from the atmosphere. And so he began to heat them, or I should say, place them in a vacuum bulb, he [had] already got a guy from New York to create his first vacuum bulbs, and then later in the summer hired a full time glass blower who was crucial to the development of the vacuum technology they used at Menlo Park. But what he eventually discovered was that it wasn't the gas, or the oxygen in the air that was affecting the bulbs so much, as it was that the gas in the metal itself was creating a problem.
So he developed this process of driving off the gases as he heated it in the vacuum and this, in fact, improved the platinum significantly where he didn't need the kind of regulators that he had to try and keep the current from getting too high, because it raised the melting point.
But platinum lamps didn't give him very high resistance, they were still not lasting as long as he wanted, and eventually he decided to try carbon again. And one of the reasons for this may be that he had been working on the telephone during the summer and the lampblack that he was using could be rolled into a very thin, wire-like substance and he began to think about trying to make wire spirals out of soft carbon. Well, the laboratory couldn't do this, but eventually what they decided to do was take a thin wire form of carbon, that is, a thread, and put that in a lamp and see what happened.
PI: Well, they took this thread, they put it in a lamp and they heated it up and they discovered that it was lasting much longer than any of the lamps they'd had up to that point. After about 13 and a half hours, where they were getting a nice glow with a fairly high resistance lamp, they decided to see what would happen if they really kicked up the current. And after a couple of hours, it finally burned out. But they realized now, they were on to something. And sometime after they began to work with carbon, you see Francis Upton draw a little cartoon figure in the notebooks, where he basically, you know, shows a lamp that's sort of got a human face on it, and underneath he writes, there's millions in it, because they realized they were really on to the future of electric lighting.
PI: By the time he'd finally developed this carbon bulb that worked, that is, that it was high resistance, it lasted for a relatively long time, he realized what he needed to do next was to find the best substance, so he began a literature search to find out what kinds of carbons would be best suited. He just determined that tall grasses with long uniform fibers would be good, eventually turning to bamboo from Japan as the best substance, and this became the commercial lamp, but it took him, you know, several months of continuing work to develop better and better lamps, so he that was getting long life lamps. And at the same time, he'd already begun to develop the system in the spring and summer of '79, before he developed the carbon lamp, he'd already improved his generator, for the system. He'd begun to work on other components, and once they had this lamp, once they demonstrated it to the public at the end '79, then 1880 become the development year. And they spent a year developing underground conductors, better meters, fixtures, improving the bulb, improving the generator, developing motors.
PI: Well after a couple months of real intensive work to develop a better and better carbon bulb, Edison had told a reporter friend for the New York Herald about the work that he had done and this guy had published a story somewhat prematurely so Edison realized he needed to demonstrate this bulb to the public and to his investors much more quickly than he had originally planned.
So they quickly hurried to install poles at Menlo Park. They got permission from Western Union to use some old poles to string the wires, although he eventually wanted them underground. They put up street lights they wired all the buildings, the laboratory, Edison's house, Francis Upton's house, and Sarah Jordan's boardinghouse where the workmen lived.
And they brought in the investors and they began to show the light off. So these fellows from Western Union came out on special trains and they were taken in to view the lamps and they were astounded by what Edison had accomplished. And it wasn't just the people from Western Union. Jay Gould showed up on one occasion, and then eventually the public began to come out to see what was going on in Menlo Park, and so they decided that they needed a full scale demonstration to the public, and so they decided that on New Year's Eve, they would have a full scale demonstration, and special trains came out from New York, and crowds of people came to Menlo Park to see this wondrous display of these soft white lights all over the landscape and in the buildings.
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