*     The present volume has employed a mosaic pattern of 
perception and observation up till now. William Blake can 
provide the explanation and justification of this procedure. 
Jerusalem , like so much of his other poetry, is concerned with 
the changing patterns of human perception. Book II, chapter 
34, of the poem contains the pervasive theme:

     If Perceptive organs vary, Objects of Perception
          seem to vary:
     If the Perceptive Organs close, their Objects seem to 
          close also.

Determined as he was to explain the causes and effects of 
psychic change, both personal and social, he arrived long ago 
at the theme of The Gutenberg Galaxy :