Benjamin Franklin

Benjamin Franklin was born in Boston in 1706, the fifteenth child of a candle-maker. He left school at ten, apprenticed to his brother as a printer at twelve, and by twenty-three owned the most successful print shop in Philadelphia. Poor Richard's Almanack made him rich; the Pennsylvania Gazette made him famous; and by the time he was forty he had earned enough to retire from business and spend the rest of his life on science, diplomacy, and the founding of a country.

His electrical work began in 1746, when a travelling demonstrator left him with a Leyden jar and a set of parlour tricks. Within six years he had rewritten the subject. Franklin argued that electricity was a single fluid — not two as his rivals believed — and that every object held either an excess of it (which he labelled "positive") or a deficit ("negative"); charging one body necessarily uncharged another by the same amount, so electric charge was conserved. The sign convention stuck even though, a century and a half later, we discovered the electron carries what he had arbitrarily called the negative sign. In June 1752 he flew a kite into a thunderstorm, drew a spark from a key tied to the soaked string, and proved lightning was nothing more than a very large electric discharge. The lightning rod followed a year later and is still the reason skyscrapers and church steeples survive storms.

The Royal Society awarded him the Copley Medal in 1753. Harvard and Yale gave him honorary degrees. When he sailed to London in 1757 as Pennsylvania's agent, he was already the most famous American alive. He later negotiated the alliance with France that won the Revolution, helped write the Declaration of Independence and the Constitution, and published the first American paper on demography. By the time he died in 1790 the streets of Philadelphia were lined with twenty thousand mourners — a quarter of the city's population. Few lives have touched more of what came after: the words "positive" and "negative" on every battery, the conservation law at the base of every circuit, and the rod still standing on every spire owe him a direct debt.