It’s freely available from Project Gutenberg.

https://www.gutenberg.org/ebooks/79003

The edition referenced in the article removes the last 4 chapters (13–16)

Off topic, but what kind of ego does it take to write an introduction that gets your name on the cover of an abridged edition? Certainly, a writer might conceive of a work as having 10 chapters and being complete, only for a publisher to demand 3 more to satisfy the expectations of the market or some literary superstition. But having been written, the text exists. It seems extremely presumptuous to me for a literary critic to take on the curatorial role and say 'you don't need to read the last quarter of the book, it's boring/repetitive.'

I find this comment valuable because it sheds light on how impressive the book is to read in contrast to the subdued treatment in the article.

Progress (as in The Pilgrim's Progress) used to mean just moving along in some travel, no positive or negative connotation to it.

It was only after the XVI century (when they still debated if the ancients or moderns were greater) that it acquired its present quasi-religious meaning, because on a short-term scale "historical progress" meant improvements in living conditions.

Because Stapledon influenced Foundation directly, acknowledged by Asimov in his own autobiography.