The book is simply fantastic! It is, as far as I'm concerned, the last word on rotary engines. It's a slim volume, but very complete and exceptionally informative.
Nahum's style is direct and conversational. He presents technical concepts in a way that is easy to understand and his arguments about how and why rotary engines fell from use so quickly after the war are well-informed and very compelling.
In the process of describing the history and function of rotary engines, Nahum debunks the persistent myths that follow nearly every mention of these types of engines regarding castor oil, the lack of throttles, etc.
I got my copy very inexpensively from an independent bookseller through Amazon.