"Cargo Cult Science". Richard P. Feynman's Caltech commencement address (1974), as quoted in "'Surely You're Joking, Mr. Feynman!': Adventures of a Curious Character" edited by Ralph Leighton (p. 342), calteches.library.caltech.edu. 1985.
"The Feynman Lectures on Physics". Physics textbook by Richard P. Feynman, Robert B. Leighton, and Matthew Sands, volume I; lecture 44, "The Laws of Thermodynamics"; section 44-1, "Heat engines; the first law"; p. 44-2, 1964.