When Edison was testing filaments he looked for materials that did not melt easily when heated. He also discovered that he wanted materials that had a high resistance. Resistance is a measure of how well a wire prevents the passage of electricity through the wire. In order to increase the resistance of a metal wire, Edison created coiled filaments, so a longer wire could be used in the same space. (Longer wires have a higher resistance.)
Iridium is a hard, brittle metal which is found in platinum ores. It has an extremely high melting point (2410┬╛C).
