The Big Book of Arcane Sciences is a publication in Fallout: Equestria.
The Big Book of Arcane Sciences is a massively comprehensive text on the subject of Arcane Sciences (a.k.a. Magic). The book likely was used as a learning aid for unicorns in the classrooms of stables and may have provided some information regarding the use of magical technology (i.e. terminals). Littlepip takes a copy of the book with her in case she gets bored when she leaves Stable 2.
Behind the Scenes
The Big Book of Arcane Sciences is a reference to the Big Book of Science which appears in the majority of Fallout games.