It is an excellent series, especially if you research that sort of thing alot. Excellent pictures and a well balanced look at the subjects. There are actually 32 books in the set as well as a Master Index. I myself am still missing "Alien Encounters", "Earth Energies", "Eastern Mysteries", "Mystic Quests", "The Mystical Year", "Search for Immortality", "Time and Space" and "Witches and Witchcraft".
I still comb used bookstores in search of those particular ones in order to have a complete set, something that apparently few have done.