A wave of Mysticism is passing over the civilised nations. It is welcomed by many: by more it is mistrusted. Even the minds to which it would naturally appeal are often restrained from sympathy by fears of vague speculative driftings and of transcendental emotionalism. Nor can it be doubted that such an attitude of aloofness is at once reasonable and inevitable. For a systematic exaltation of formless ecstasies, at the expense of sense and intellect, has a tendency to become an infirmity if it does not always betoken loss of mental balance. In order, therefore, to disarm natural prejudice, let an opening chapter be devoted to general exposition of aims and principles.