"An admirable introduction to the rigorous theory of the continuum." — Science Progress "Extremely readable . . . a clear axiomatically constructed introduction." — Elemente der Mathematik This classic of mathematics presents the best systematic elementary account of the modern theory of the continuum as a type of serial order. Based on the Dedekind-Cantor ordinal theory, this text is suitable for advanced undergraduates and graduate students in mathematics and requires no knowledge of higher mathematics. The treatment begins with a historical introduction, followed by chapters on classes in general; simply ordered classes, or series; discrete series, especially the type of the natural numbers; and dense series, especially the type of the rational numbers. Subsequent chapters explore continuous series, especially the type of the real numbers; continuous series of more than one dimension, with a note on multiply ordered classes; and well-ordered series, with an introduction to Cantor's transfinite numbers. An Index of Technical Terms concludes the text.