Amazon.com:
Here is a book to intrigue both non-technical and more mechanically inclined UFO enthusiasts. Without making a case for the origins of UFOs, Hill argues that their functionality is feasible by applying established principles of physics to existing reports in which an amazingly consistent UFO behavior has been described. In language which is technically sound, but not so advanced that the layman could not understand, Hill works out several possible propulsion systems for these mysterious craft.