In theory, this book tracks the influence of "the occult" oon literature, art, science…
Needless to say, that's a slightly difficult task – by nature, and by definition, "the occult" is hidden.
Having said that, I enjoyed this book, and found it useful. There are times when the writer is more credulous than I am (I'm not at all sure I believe as much about some of the historical figures as he does), but not overly so – this is still within the realms of "read with some confidence".
For those who are new to the area, this book might assume more knowledge than is comfortable – for those who know the area well, the book will be vaguely interesting but will tell them little new. For those who have some background, but not much – it might just be a gold mine.
It has a serious lack, however, in not having an index – one must trawl through to find entries. Admittedly, these are fairly well marked but the lack of an index reduces the usefulness of the book greatly.