Cox wrote several books including "Why We Laugh," "A Buckeye Abroad" (1852), "Eight years in Congress, from 1857 to 1865" (1865) and "Three Decades of Federal Legislation, 1855-1885" (1885). His colleagues appreciated him most for his ready sense of humor, usually gentle rather than cutting. Indeed, some of them thought that his joking quality may have kept him from becoming Speaker of the House, because, for all his hard work and studious habits, he was not taken seriously. "In his political action he seemed more anxious to annoy his opponents than to extinguish them," Congressman George S. Boutwell of Massachusetts wrote, in a typical dismissal. "His speeches were short, pointed and entertaining. He was a favorite with the House, but his influence upon its action was very slight. Those who acquire and retain power are the earnest and persistent men. When Cox had made his speech and expended his jokes he was content. The fate of a measure did not much disturb or even concern him." Cox once whimsically suggested that those supporting a high protective tariff duty on foreign coal should likewise lay a heavy duty on the sun, as a dangerous competitor in warming people up.