Annie Besant 
The Nature and Practice of Yoga [EPUB ebook] 

A complete essential introduction to Yoga theory and practice designed as series of lessons covering all key elements such as nature, body, mind, spirituality, different schools of thought, yoga science, and yoga practice. The author is aiming to prepare the student to take up, for practical purposes, the Yoga sutras. The lessons, may, however, also give to the ordinary lay reader some idea of Yoga, and perhaps to allure a few towards its study.