In Memory Yet Green (1920-1954)
In Joy Still Felt (1954 - 1978)
Each of these volumes was well over 800 pages. Why did Asimov choose to break up the volumes in the year 1954.
Well, it was in 1954 that he turned 35. As he says in the intro to Volume 2:
I had reached mid-life, for I was approachimg my 35th year, halfway to three-score and ten. (Asimov was an atheist, but for some reason the fact that the bible said people should live to age 70 weighed upon him.
[From The Phrase Finder: The span of a life. In the days that this was coined that was considered to be seventy years.
Threescore used to be used for sixty, in the way that we still use a dozen for twelve, and (occasionally) score for twenty. It has long since died out in that usage but is still remembered in this phrase.]
I had reached what seemed to be the peak of possible--and it wasn't enough.
In my professional career as a chemist, I had finally achieved professorial status, but my position was very low-paying and I didn't see that I could possibly advance either in renumeration or reputation very much beyond the point I had reached.
In my professional career as a writer, I had become a first-rank science fiction writer as early as 1941, but even after more than a decade of constant success both in magazine short stories and and in hard-cover novels, my earnings as a writer were moderate, and I didn't see any possibility of increasing them further, or of gaining any reputation outside the constricted boundaries of science fiction.
I had, in short, reached a blank wall, a dead in.
And yet I managed to overleap the blank wall and burrow through the dead end and to reach both an income and a reputation which to me, in 1954, would have been inconceivable. The story of how I I did this is contained in this second volume...