The Fourth "R" (a.k.a. The Brain Machine) is a science fiction novel by George O. Smith first published in 1959.

He looked like a harmless kid, but locked in his mind was a time bomb!

It is a science fictional examination of the genius naïf phenomenon. The plot follows a five-year-old boy named Jimmy Holden, who was given the equivalent of a college education by virtue of his parents' invention, an "Electromechanical Educator."

The novel was a digression from his focus on outer space, and provides one of the more interesting examinations of a child prodigy in science fiction.

In his review column for F&SF, Damon Knight selected the novel as one of the 10 best genre books of 1959. R. D. Mullen reported that “Though it becomes tendentious and sentimental in its last chapters, “The Brain Machine” is up to that point a surprisingly good story of the difficulties of the superboy in a world run by stupid adults.” 

The book was first published by Ballantine Books in 1959 as The Fourth "R", a paperback original. It was reprinted by Lancer Books in 1968 and then by Garland Press in 1975 in hardcover as The Brain Machine. It was reprinted again by Dell under its original title, The Fourth "R", in 1979.

The book is not related to the movie The Brain Machine (1977).

George Oliver Smith (1911-1981) (also known by the pseudonym Wesley Long) was an American science fiction author. He is not to be confused with George H. Smith, another American science fiction author.

Smith wrote mainly about outer space, with such works as Operation Interstellar (1950), Lost in Space (1959), and Troubled Star (1957). Smith continued regularly publishing science fiction novels and stories until 1960. He was given the First Fandom Hall of Fame award in 1980.