Yogi Ramacharaka 
Hatha Yoga – The Yogi Philosophy of Physical Wellbeing [EPUB ebook] 

The whole theory and practice of Hatha Yogi is based upon this idea of return to nature—the belief that the Instinctive Mind of man contains that which will maintain health under normal conditions. And accordingly those who practice its teachings learn first to ‘let go, ‘ and then to live as closely to natural conditions as is possible in this age of artificiality. And this little book has been devoted to pointing out nature’s ways and methods, in order that we may return to them. We have not taught a new doctrine, but have merely cried out to you to come with us to the good old way from which we have strayed.