A Key to Polite Literature (1763)
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An early handbook to classical literature and mythology. Not exactly sure what makes it "polite" for anybody with even passing familiarity with the subject but more likely that's a meaning shift. A contemporary review says "equally useful and entertaining to those who have not opportunity and inclination to consult more particular accounts of the heathen mythology". (Critical Review, April 1763) It was originally issued at The Gentleman and Lady's Key to Polite-Literature. The author(s) are unknown and at least one later bibliographer has improbably considered it children's literature.
The value of such older reference works both their different viewpoints and the sometimes unusual information they contain. The very first entry here, for instance, is something I didn't know - "Abadir" was the name of the stone given to Saturn (Cronos) which he consumed instead of his son Jupiter (Zeus). That story is familiar enough but the name of the stone? Why did it even have a name? Turns out this is more commonly called the Omphalos stone though I can't find any documentation for the name used here. In any case, the book is well worth browsing if this sounds at all like anything of interest to you.