Richard Courant 
Supersonic Flow and Shock Waves [PDF ebook] 
A Manual on the Mathematical Theory of Non-Linear Wave Motion

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. Chapter II develops a theory of the type of partial differential equations which occur in treatable problems of compressible flow; An important point is the emphasis on what the authors call simple waves, representing motion in domains adjacent to domains of constant state.