Today is the anniversary of the death in 1991 of Harry Everett Smith. Most famous as the compiler of the Anthology of American Folk Music, he was also an experimental film maker.
Early Abstractions is considered "culturally, historically, or aesthetically significant" by the Library of Congress. FilmPreservation.org has some information. Here are Early Abstractions videos from youtube:
"No. 11: Mirror Animations" is only online is an edited form. This clip includes the first 2/3 of the film:
Senses of Cinema has an article. HistoryLink.org has an overview of his life and work. There is an article on the Harry Smith Archives here. A video on the restoration and reformatting of "Mahagonny" can be viewed here. His films are relatively inaccessible, not being widely available on DVD.