The Victor Book of the Opera (1913)
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By 1913 the Victor Talking Machine Company already had a thousand opera records, at least according to this book. Turns out those are arias not complete operas and according to this book some cost as much as $3. The Victor Book of the Opera serves as both a catalog and a reference work. Opera buffs will not only enjoy the descriptions (more than mere plot synopsis) but also the numerous illustrations of both costumes and staging. It's also interesting for the works mentioned that appear to have fallen by the side. I've never heard of Ambroise Thomas' Mignon and am pretty sure Massenet's Hérodiade is rarely discussed today but then I'm hardly an opera expert and could well be wrong.