There have been for ages past in India and other Oriental countries men who devoted their time and attention to the development of Man, physically, mentally and spiritually. The experience of generations of earnest seekers has been handed down for centuries from teacher to pupil, and gradually a definite Yogi science was built up. To these investigations and teachings was finally applied the term "Yogi," from the Sanscrit word "Yug," meaning "to join," From the same source comes the English word "yoke," with a similar meaning. Its use in connection with these teachings is difficult to trace, different authorities, giving different explanations, but probably the most ingenious is that which holds that it is intended as the Hindu equivalent for the idea conveyed by the English phrase, "getting into harness," or "yoking up," as the Yogi undoubtedly "gets into harness" in his work of controlling the body and mind by the Will.
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. In the work we 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.