James Watt

James Watt (1736-1819) of Scotland, whose last name appears on every lightbulb, started his career at age 23 in partnership with John Craig, an architect, and businessman. The company manufactured and sold several products, including musical instruments and toys, and lasted into the 20th century.

Watt was interested in steam engines and dramatically improved their efficiency by adding a separate condensing chamber. A further refinement allowed his steam engine to deliver rotary power, which greatly broadened its usefulness. He developed the unit of horsepower to compare the output of the steam engines with that of draft horses.

In electrical terms, the watt was initially defined as “the power conveyed by a current of one ampere through the difference of potential of one volt.”

Power is a rate, much like speed is a rate. For example, mph tells you how far you have traveled for a given amount of time. A watt shows how much energy is spent or transferred with respect to time.

Fun facts: Watt, a private person, turned down a knighthood. A few years after he died, the public paid for a statue of him to be erected in Westminster Abbey.