This book has been written in an attempt to provide a satisfactory
textbook to be used as a basis for elementary courses in Non-Euclidean
Geometry. The need for such a volume, definitely intended for classroom
use and containing substantial lists of exercises, has been evident for
some time. It is hoped that this one will meet the requirements of those
instructors who have been teaching the subject regularly, and also that
its appearance will encourage others to institute such courses. The
benefits and amenities of a formal study of Non-Euclidean Geometry are
generally recognized. Not only is the subject matter itself valuable and
intensely fascinating, well worth the time of any student of
mathematics, but there is probably no elementary course which exhibits
so clearly the nature and significance of geometry and, indeed, of
mathematics in general. However, a mere cursory acquaintance with the
subject will not do. One must follow its development at least a little
way to see how things come out, and try his hand at demonstrating
propositions under circumstances such that intuition no longer serves as
a guide.