1st edition:
https://www.goodreads.com/book/show/13558287-only-connect

2nd edition: https://www.goodreads.com/book/show/2556253.Only_Connect

The third edition does not appear to have that essay, judging from WorldCat.

One of my favorite essays! I first read it at age 19 in Only Connect, and it shaped me as a writer.

I also love her 1971 essay "History is People," which was reprinted in Virginia Haviland's Children and Literature: Views and Reviews.

https://www.goodreads.com/book/show/4694006-children-and-literature

Here's an excerpt:

http://engl2011-childrensliterature.blogspot.com/2013/04/rosemary-sutcliff-1920-1992.html