Many other substances were tried, even human hair.

Edison concluded that carbon of some sort was the solution rather than a metal.

Almost coincidently, Swan, an Englishman, who had also been wrestling with this problem, came to the same conclusion.

Finally, one day in October, 1879, after fourteen months of hard work and the expenditure of forty thousand dollars, a carbonized cotton thread sealed in one of Edison's globes lasted forty hours.

"If it will burn forty hours now," said Edison, "I know I can make it burn a hundred." And so he did.