Yogi Ramacharaka 
A Series of Lessons in Gnani Yoga (The Yoga of Wisdom) [EPUB ebook] 

‘The Yogi Philosophy may be divided into several great branches, or fields. What is known as ‘Hatha Yoga’ deals with the physical body and its control; its welfare; its health; its preservation; its laws, etc. What is known as ‘Raja Yoga’ deals with the Mind; its control; its development; its unfoldment, etc. What is known as ‘Bhakti Yoga’ deals with the Love of the Absolute-God. What is known as ‘Gnani Yoga’ deals with the scientific and intellectual knowing of the great questions regarding Life and what lies back of Life-the Riddle of the Universe.’ So begins ‘A Series of Lessons in Gnani Yoga (The Yoga of Wisdom)’ by Yogi Ramacharaka.