Richard Cohen in Lapham’s Quarterly:
William Ewart Gladstone was Britain’s prime minister four times between 1868 and 1894, a member of Parliament for more than sixty years, a brilliant and passionate orator, an accomplished writer, and an indefatigable social reformer. Lord Kilbracken, his private secretary, estimated that if a figure of 100 could represent the energy of an ordinary man and 200 that of an exceptional one, Gladstone’s energy would be represented by a figure of at least 1,000.
…There are over a dozen common forms of energy, as usually itemized, from chemical, gravitational, and electromagnetic to nuclear, thermal, and wind. It is a formidable register—but human energy rarely appears in such listings. When set against those other categories, what do we mean by the term, anyway? The word energy itself comes from the ancient Greek ἐνέργεια, meaning “activity.” Aristotle said it was a condition that describes the capacity to do work. More recently, human energy has been similarly defined as the amount of stamina, vigor, or “juice” a person has to engage in a particular activity. None of this, unfortunately, takes us very far. There is obviously a difference between a person full of gusto and joie de vivre and a person with significant actual productivity. Marcel Proust spent much of his adult life lying in bed, but his masterwork, À la recherche du temps perdu, has 1,267,069 words in it, double the number in War and Peace. Voltaire spent eighteen hours a day writing or dictating to secretaries, eventually completing an output covering two thousand works; he sustained himself by drinking, so it was said, fifty cups of coffee a day. But while such prodigious feats are all about get-up-and-go, it is not something, a chemical reaction, but someone who has to do the getting up and going.
More here.