Mark Twain's phrenological experiment: Three renditions of his "small test".

Samuel Langhorne Clemens (1835-1910), the American humorist and author better known as Mark Twain, was skeptical about clairvoyance, supernatural entities, palm reading, and certain medical fads, including phrenology. During the early 1870s, he set forth to test phrenology-and, more specifically, its reliance on craniology-by undergoing two head examinations with Lorenzo Fowler, an American phrenologist with an institute in London. Twain hid his identity during his first visit, but not when he returned as a new customer three months later, only to receive a very different report about his humor, courage, and so on. He described his experiences in a short letter written in 1906 to a correspondent in London, in humorous detail in a chapter that appeared in a posthumous edition of his autobiography, and in , a work of fiction involving time travel, which he began to write around 1901 but never completed. All three versions of Twain's phrenological ploy are presented here with commentary to put his descriptions in perspective.