The main theme of this best-selling book is that the transmission of energy by wave propagation is fundamental to almost every branch of physics. Therefore, besides giving students a thorough grounding in the theory of wave and vibrations, the book also demonstrates the pattern and unity of a large part of physics. This new edition has been thoroughly revised with the help of Professor Lyle Roelofs of Haverford College, USA. As with earlier editions, there are large numbers of problems together with hints on how to solve them.