The word "energy" entered English and other European languages in the sixteenth century from Aristotle's writings, and was restricted to meanings close to his until the nineteenth century. The total entry for "Energy" in the first edition (1771) of the Encyclopaedia Britannica is as follows: "A term of Greek origin signifying the powers, virtues or efficacy of a thing. It is also used figuratively, to denote emphasis of speech." These meanings survive; Swift's energetic pronouncement in 1720 that "Many words deserve to be thrown out of our language, and not a few antiquated to be restored, on account of their energyand sound" still rings a bell. But they are no longer dominant. Stronger by far is the scientific meaning, fixed between 1849 and 1855 by two men, William Thomson (the future Lord Kelvin) and W. J. Macquorn Rankine, professors, respectively, of natural...