October 2004 | Volume 55, Issue 5
The experiments of October 21 yielded the first truly promising results for the weary lab workers. Most notably, when a filament made of ordinary thread was carbonized and hooked up to an electrical circuit, it glowed from 1:30 A.M. to 3:00 P.M. After the power was increased, it shone even brighter for another hour before finally breaking. Here was the first clear evidence that Edison and his men were on the right track, and they worked eagerly to improve and refine their design. By the end of the year, they had the technology well enough under control to make a grand public demonstration with more than 50 shining bulbs.
Little of what went into Edison’s electric light was completely new. Researchers had been trying to make incandescent lights since 1820, mostly with spirals of thin platinum wire, which was chosen for its high melting point. In 1860 the British scientist Joseph Swan patented an incandescent lamp with a carbonized paper filament, and by the late 1870s he, too, was getting excellent results with carbonized cotton thread.
Still, there was enough novelty in Edison’s design to justify a patent, which he quickly took out. Until it expired, he dominated the American market for electric lighting, supplying about 75 percent of the nation’s bulbs along with, in many cases, the power to light them. Swan controlled most of Britain’s electric-lighting business until his company and Edison’s British subsidiary merged in 1883. Edison rolled up 1,093 patents before he was finished inventing, while Swan, who had previously invented the dry photographic plate, did not do badly either, developing a process for making artificial fibers that remains in use in the textile industry to this day.