In late fifteenth century Florence, Renaissance humanists rediscovered a secret, natural language hidden in the visual wisdom of the proverb 'the eyes are the windows of the soul'. Through its magical prism, the language of eyes, faces, voices, laughs, walks, even stones, plants and animals, all became windows into the souls of other people, of oneself, of nature, and ultimately of God. Some saw in its words the perfect hieroglyphic language by which Adam had first named nature, which, when combined with the art of memory, could bring about a form of 'inner writing' or mystical...