Underhill Evelyn 
Revival: Mysticism (1911) [PDF ebook] 

This book falls naturally into two parts: each of which is really complete in itself, though they are in a sense complementary to one another. Whilst the second and longest part contains a somewhat detailed study of the nature and development of man’s spiritual or mystical consciousness m the first is intended rather to provide an introduction to the general subject of mysticism. Exhibiting it by turns from the point of view of metaphysics, psychology, and symbolism, it is an attempt to gather between the covers of one volume information at present scattered amongst many monographs and texts books written in divers tongues, and to give the student in a compact form at least the elementary facts in regard to each of those subjects which are most closely connected with the study of the mystics.