Yoga is divided into several branches, ranging from that which teaches the control of the body, to that which teaches the attainment of the highest spiritual development. This work will not go into the higher phases of the subject, except when the "Science of Breath" touches upon the same. The "Science of Breath" touches Yoga at many points, and although chiefly concerned with the development and control of the physical, has also its psychic side, and even enters the field of spiritual development. The Hindu Yogis have always paid great attention to the Science of Breath, for reasons which will be apparent to the student who reads this book. Many Western writers have touched upon this phase of the Yogi teachings, but we believe that it has been reserved for the writer of this work to give to the student, in concise form and simple language, the underlying principles of the Yogi Science of Breath, together with many of the favorite Yogi breathing exercises and methods. We have given the Western idea as well as the Oriental, showing how one dovetails into the other. We have used the ordinary English terms, almost entirely, avoiding the Sanscrit terms, so confusing to the average Western reader. The first part of the book is devoted to the physical phase of the Science of Breath; then the psychic and mental sides are considered, and finally the spiritual side is touched upon.