The Garland of Letters
Livre de Sir John Woodroffe (Arthur Avalon)
The Garland of Letters: Studies in the Mantra-Shastra by John Woodroffe (Arthur Avalon). Not really a work on Mantra-Yoga, in order to explain why the use of Mantra is not senseless superstition, Woodroffe has to more or less describe the creation of the universe and the evolution of consciousness as conceived of by the S'âkta schools pretty much from first principles. Not an easy read, but it's not an easy subject.