I was fortunate to receive help from many. Professor Sir James Lighthill FRS provided the impetus to undertake this venture. Dr Allen Tayler helped my rather amorphous ideas assume a precise form. Professor A. Richard Seebass, many years ago, introduced me to the mysteries of Burgers' equation and its kindred class. I had the benefit of very fruitful discussions with Professors D. G. Crighton and J. D. Murray. Professor Colin Rogers read through parts of the manuscript. Professors P. N. Kaloni and M. C. Singh were excellent hosts during my sojourns at the Universities of Windsor and Calgary, where I wrote part of the book. My student, Mr K. R. C. Nair, carried out much of the computations reported in the final chapter and assisted in various other ways. Ms Thelma Stanley, with good cheer and patience, typed the manuscript and many a change I made in it. Finally, I owe a lot to my wife Rita, who cared and comforted.

I gratefully acknowledge the financial assistance provided for the preparation of the manuscript by the Curriculum Development Cell, established at the Indian Institute of Science by the Ministry of Education and Culture, Government of India.

In conclusion, I thank Dr David Tranah of Cambridge University Press, for his courtesy and thoughtful consideration during the entire course of the publication of this monograph.