by Yogi Ramacharaka (William Walker Atkinson)
Raja Yoga is about using techniques such as meditation, retention of breath, and concentration to achieve the ultimate goal of absorption into the cosmos. However, like most of the Yogi Publications books written and published by William Walker Atkinson under a pseudonym, this is basically a New Thought tract. Apparently this was originally a correspondence course in mental focus, which he repurposed under one of his Hindu pseudonyms to fill in the Raja Yoga slot in the YPS lineup.
The book, strangely, is titled 'Raja Yoga, or Mental Development' on the cover, and 'A Series of Lessons in Raja Yoga' on the title page, another clue to the repackaging job. The core of the book is a number of mental exercises and affirmations, only peripherally related to traditional yogic practice. There are numerous uncited quotes from western authors, but the only actual Hindu author he quotes is Edward Carpenter, which doesn't make a good case for an Indian hand at work here. As is typical in the YPS books, there are long digressions on science, just as modern New Thought proponents reference quantum physics. Atkinson does not mention asanas (yogic postures) or breathing exercises, key techniques which are used in Raja and other schools of Yoga. For more information on Raja Yoga, refer to the chapter Râja Yoga in How to be a Yogi of Swami Abhedânanda , as well as Relax With Yoga by Arthur Liebers , which discusses modern western Raja Yoga.