THE BOOK DEPARTMENT of Scientific American is conducted, with the co-operotion of the Editors, to make available for you o comprehensive book service. Each month the Editors select ond review in these columns new books in a wide range of scientific ond technical fields. In addition, they are ready at all times to advise you regording the best available books on any subject. You ore invited to use this service freely. Tell our Book Department what kind of books you want ond you will be furnished with a list of available titles, including prices. When inquiring obout books, please be specific; remember that we con be of the greotest help only when you tell us just whot you ore looking for. Books listed in these columns moy be ordered from our Book Department.