Two years after her success in the Moral Sciences Tripos (two examiners placed her in the First class and two in the Second), Mary Paley was asked to write an economics textbook for Extension Lecture students. On her engagement, the book became a joint effort with her fiance, later husband, Alfred Marshall. It was published in October 1879 and reprinted nine times between 1879 and 1891, including a revised edition in 1881. A third edition was worked on, probably around 1885, but not published. According to John Maynard Keynes, 15,000 copies of the book were sold in all (Pigou 1925, p. 500). Sometime in the late 1880s or early 1890s, Marshall rejected the book, criticizing its elementary nature and brevity—it was impossible, he felt, “to tell the truth for half-a-crown” (M. P. Marshall 1947, p. 22). When he sent his brother-in-law, E. D. Guillebaud, a complimentary copy of the Principles in 1890, Marshall stipulated that the Economics of Industry must be returned for destruction (Guillebaud 1961,2, p. 12, note c). In 1892 he produced a small book “made chiefly by scissors and paste out of my Principles,” which on its spine bore the title Economics of Industry.