At the time of Alexander Graham Bell and Thomas Watson's first successful telephone transmission in 1875, the only wires strong enough to be strung over long distances were made of iron. Iron wires had been used for telegraph systems but they were unsuitable for long-distance telephone links. But, in 1877, an American, Thomas Doolittle, developed a method of manufacturing copper wires strong enough to be strung between telegraph poles. Copper's superior conductivity preserved the integrity of the telephone signal to an extent that iron could not. The age of mass communications was born.

• Jeremy Clarkson