In reviewing the mental and spiritual activity of the human race, Dr. Bucke discovers that at intervals certain individuals have appeared who are gifted with the power of transcendent realization—or Illumination. Their experiences constitute a definite advance in man’s relation with the Infinite. Moreover, the author shows from available records that this transfiguring endowment of Illumination is on the increase, and he gives full details of practically all the cases on record up to the time when the book was written.