On January 26, 1945, I began "The Mule," my personal favorite among the Foundation stories, and the longest yet, for it was 50,000 words. It was printed as a two-part serial (the very first serial I was ever responsible for) in the November and December 1945 issues. By the time the second part appeared I was in the army.

After I got out of the army, I wrote "Now You See It-" which appeared in the January 1948 issue. By this time, though, I had grown tired of the Foundation stories so I tried to end them by setting up, and solving, the mystery of the location of the Second Foundation. Campbell would have none of that, however. He forced me to change the ending, and made me promise I would do one more Foundation story.

Well, Campbell was the kind of editor who could not be denied, so I wrote one more Foundation story, vowing to myself that it would be the last. I called it "-And Now You Don't," and it appeared as a three-part serial in the November 1949, December 1949, and January 1950 issues of Astounding.

By then, I was on the biochemistry faculty of Boston University School of Medicine, my first book had just been published, and I was determined to move on to new things. I had spent eight years on the Foundation, written nine stories with a total of about 220,000 words. My total earnings for the series came to $3,641 and that seemed enough. The Foundation was over and done with, as far as I was concerned.

In 1950, however, hardcover science fiction was just coming into existence. I had no objection to earning a little more money by having the Foundation series reprinted in book form. I offered the series to Doubleday (which had already published a science-fiction novel by me, and which had contracted for another) and to Little-Brown, but both rejected it. In that year, though, a small publishing firm, Gnome Press, was beginning to be active, and it was prepared to do the Foundation series as three books.