This book is a classic in the field of rational consideration of psychic and mystical experiences — written by a British-born physicist and master of a college in an Australian university. Many references to the book have appeared in the text and footnotes of later books. Johnson surveys the best of scientific, anecdotal, and theoretical sources, offering insights from this material. I’ve re-read it from time to time since maybe 1995 or so, and found it absorbing. Yet, being a serious book, solidly packed with information, it may seem a bit dry to some readers.