The Doctrine and Practice of Yoga - Mukerji swámi A. P.

This is a great book for understanding the concepts of yoga. It includes the Practices and Exercises of Concentration, both Objective and Subjective, and Active and Passive Mentation, an Elucidation of Maya, Guru Worship, and the Worship of the Terrible, also the Mystery of Will-Force.

Swami Mukerji was a Yogi of the South India Order.