This book unquestionably shows the PHYSICAL nature of many UFOs - that these things are big and heavy - when landed at least. He discusses "UFO nests" where they swirl when they land on grass, etc. He also says that when UFOs land on marshy ground they do a "belly flop" and distribute their weight over a larger area. By measuring the compression of the mud they can ascertain certain things. He says that "when landed" these things have a tremendous weight.