Seit dem 1.1.2022 ist die 13. Auflage der Encyclopedia Britannica gemeinfrei. 1926 erschienen drei neue Bände als Supplement zur 11. Auflage, die seit den 2000er Jahren gemeinfrei ist (via Researchbuzz: Firehose und Reddit):
«Three new volumes published in 1926 replaced the 12th edition as a supplement to the 11th edition. The new volumes, together with the reprinted 11th edition, constituted the 13th edition. The new volumes were numbered 29 to 31, the 29th volume of the 11th edition becoming the 32nd volume of the 13th edition.
You can easily find PDFs of the 11th edition out there since it’s been public domain since the 2000s, so with the addition of these three volumes, you can have the entire 1926 Britannica on your hard drive legally and free of charge!
The list of authors includes some pretty notable names like Albert Einstein, W.E.B. DuBois, Guglielmo Marconi, Leon Trotsky and George Eastman. This alone should cement its value as a historical record of opinion and expertise of the time period. It goes without saying that many of the views expressed in these old volumes are outdated, but if you’re the kind of person who keeps Kiwix packages of Wikipedia around, this should be right up your alley.