Lasting knowledge comes from understanding and we have tried our best to make this book more understandable. Although mass of the book is limited, but new editions always have a tendency to grow up. Anyways, more illustrations have been added in this book. All the topics have been extensively re-viewed and then written. Some additions and a few subtractions have been made and all the knowledge is updated. So what you hold in your hands is a concentrated extract of knowledge from several text books. The hard work needed to improve a book and then getting it published was really too much but we sincerely hope that our efforts will make life easier for the students. We wish you all good luck. Tank you for your immense feed back and appreciation and we hope you will continue to help us with your remarks and suggestions.