The level of mathematics required to follow the arguments in the book is in general higher than one could expect of the average undergraduate. Rather it is aimed at postgraduate research workers and third year students specialising in mathematical physics. It should be emphasised, however, that the book contains a great deal of discussion and presentation of results which can be read without working in detail through the mathematics. This is particularly true of Chapter 5 in which are discussed some basic problems in transport theory.
One of the dangers of trying to bridge the gap between two disciplines is the possibility of incurring the displeasure of both simply by leaving out 'important' problems. Space has limited the number of problems that can be discussed and even if the author has not pleased everybody he hopes that he has chosen representative problems which illustrate the common ancestry of the two fields. He has also tried to point out areas where further research is required or where methods from one field could profitably be applied to the other.