I am extremely happy to place before the readers the 1st   edition of book. Almost all the topics have been thoroughly gone through, present lucidly and briefly, avoiding lengthy discussions but without sacrificing the theme of theories. The quality of subject matter has been improved by consulting other books in this field.

The main aim of this book is to facilitate easy understanding of the matter at one reading without any tediousness in grasping the theories.

It is my earnest hope that the students and teachers will find the new and enlarged edition more useful. Suggestions for improvement of this book are warmly welcomed.