Question: The John Downing Jr. House is a historic house in downtown Middleport, a village located on the banks of the Ohio River in the southeastern part of the U.S. state of Ohio, notably, his work with the young Samuel Clemens led to a literary appearance years later: writing under the name of "Mark Twain", Clemens portrayed him in which book, released in 1883, is a memoir by Mark Twain of his days as a steamboat pilot on the Mississippi River before the American Civil War, and also a travel book, recounting his trip along the Mississippi River from St. Louis to New Orleans many years after the War?
Sentence (from "John Downing Jr. House"): Known to his intimates as "Major" Downing, he worked for much of his life as a pilot for riverboats on the Mississippi River.
Relevant evidence: No