The Difference Engine was an early computer designed by Babbage, Charles in the first half of the 19th Century. It uses the method of 'finite differences' to calcualte polynomials, and is thus a fixed purpose calculator unlike Babbage's later designs for the Analytic Engine, the worlds first programmable computer, alas never constructed except in steam-punk fiction.
Used on Chap. 1: pages 5, 6; Chap. 14: page 334
Links:
computerhistory.org: Computer History Museum: The Engines- collection.sciencemuseumgroup.org.uk: Scence Museum: Difference Engine No. 1