My grandmother had one of those, which ended up in my parent's bookcase. Neither of my parents were much interested in music (I think the only music my father ever listened to was Gaite Parisienne), but I was a voracious reader and I read much of it, some 65 years or so ago. Like all such books, it is limited to what was at that time the common reportory, so, for instance, Nabucco, which is now current, is misssing.
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Regerds, Pete