> http://www.heracliteanriver.com/?p=324
Many thanks for pointing out that article! This reminds me of a similar discussion on typophile (http://typophile.com/node/56108) in which one of the participants (near the end of the thread) shows an interesting visual experiment with sentence space, based on a historical document. (Plus, the discussion also mentions TeX and groff.) If I may hazard a guess, it is possible that the notion of *doubling* the space did indeed come from typewriters, where spaces came in one size only. In lead typesetting there were spaces of many different widths, and the typesetter probably did not insert two "normal" spaces, but simply a larger space (e.g., a quad).
