My article “The Vis Viva Dispute: A Controversy at the Dawn of Dynamics” (Physics TodayOctober 2006, page 31) included an unfortunate historical error: René Descartes’ rules for impact all first appeared in the 1644 Latin edition of his Principia and not in the 1647 French edition, as remarked in the article. The French edition merely expanded his explanation of the rules. Although this error is irrelevant to the article’s overall argument, it is nevertheless important to correct, for such careless expositional flourishes have a way of turning into accepted fact when not corrected.